Locally distributed keyword detection

ABSTRACT

In one aspect, a playback device includes at least one microphone configured to detect a voice input and generate sound input data. The playback device detects a first command keyword in the detected sound and, in response, makes a first determination, via a first local natural language unit (NLU), whether the input sound data includes at least one keyword within a first predetermined library of keywords. The playback device receives an indication of a second determination made by a second NLU that the input sound data includes at least one keyword from a second predetermined library of keywords. The playback device compares the results of the first determination and the second determination and, based on the comparison, foregoes further processing of the input sound data.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.16/528,224, filed Jul. 31, 2019, which is incorporated herein byreference in its entirety.

FIELD OF THE DISCLOSURE

The present technology relates to consumer goods and, more particularly,to methods, systems, products, features, services, and other elementsdirected to voice-assisted control of media playback systems or someaspect thereof.

BACKGROUND

Options for accessing and listening to digital audio in an out-loudsetting were limited until in 2002, when SONOS, Inc. began developmentof a new type of playback system. Sonos then filed one of its firstpatent applications in 2003, entitled “Method for Synchronizing AudioPlayback between Multiple Networked Devices,” and began offering itsfirst media playback systems for sale in 2005. The Sonos Wireless HomeSound System enables people to experience music from many sources viaone or more networked playback devices. Through a software controlapplication installed on a controller (e.g., smartphone, tablet,computer, voice input device), one can play what she wants in any roomhaving a networked playback device. Media content (e.g., songs,podcasts, video sound) can be streamed to playback devices such thateach room with a playback device can play back corresponding differentmedia content. In addition, rooms can be grouped together forsynchronous playback of the same media content, and/or the same mediacontent can be heard in all rooms synchronously.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, aspects, and advantages of the presently disclosed technologymay be better understood with regard to the following description,appended claims, and accompanying drawings, as listed below. A personskilled in the relevant art will understand that the features shown inthe drawings are for purposes of illustrations, and variations,including different and/or additional features and arrangements thereof,are possible.

FIG. 1A is a partial cutaway view of an environment having a mediaplayback system configured in accordance with aspects of the disclosedtechnology.

FIG. 1B is a schematic diagram of the media playback system of FIG. 1Aand one or more networks.

FIG. 2A is a functional block diagram of an example playback device.

FIG. 2B is an isometric diagram of an example housing of the playbackdevice of FIG. 2A.

FIG. 2C is a diagram of an example voice input.

FIG. 2D is a graph depicting an example sound specimen in accordancewith aspects of the disclosure.

FIGS. 3A, 3B, 3C, 3D and 3E are diagrams showing example playback deviceconfigurations in accordance with aspects of the disclosure.

FIG. 4 is a functional block diagram of an example controller device inaccordance with aspects of the disclosure.

FIGS. 5A and 5B are controller interfaces in accordance with aspects ofthe disclosure.

FIG. 6 is a message flow diagram of a media playback system.

FIG. 7A is a functional block diagram of certain components of anexample network microphone device in accordance with aspects of thedisclosure.

FIG. 7B is a functional block diagram illustrating an example statemachine in accordance with aspects of the disclosure.

FIG. 8 shows example noise graphs illustrating analyzed sound metadataassociated with background speech.

FIG. 9A shows a first portion of a table illustrating example commandkeywords and associated conditions in accordance with aspects of thedisclosure.

FIG. 9B shows a second portion of a table illustrating example commandkeywords and associated conditions in accordance with aspects of thedisclosure.

FIG. 10 is a schematic diagram illustrating an example media playbacksystem and cloud network in accordance with aspects of the disclosure.

FIG. 11 is a flow diagram of an example method for locally distributedkeyword detection in accordance with aspects of the disclosure.

FIG. 12 is a flow diagram of another example method for locallydistributed keyword detection in accordance with aspects of thedisclosure.

FIGS. 13-15 illustrate examples of locally distributed keyword detectionvia multiple network microphone devices in accordance with aspects ofthe disclosure.

The drawings are for purposes of illustrating example embodiments, butit should be understood that the inventions are not limited to thearrangements and instrumentality shown in the drawings. In the drawings,identical reference numbers identify at least generally similarelements. To facilitate the discussion of any particular element, themost significant digit or digits of any reference number refers to theFigure in which that element is first introduced. For example, element103 a is first introduced and discussed with reference to FIG. 1A.

DETAILED DESCRIPTION I. Overview

Example techniques described herein involve keyword engines configuredto detect commands. An example network microphone device (“NMD”) mayimplement such a keyword engine in parallel with a wake-word engine thatinvokes a voice assistant service (“VAS”). While a VAS wake-word enginemay be involved with nonce wake-words, a command-keyword engine isinvoked with commands, such as “play” or “skip.”

Network microphone devices may be used facilitate voice control of smarthome devices, such as wireless audio playback devices, illuminationdevices, appliances, and home-automation devices (e.g., thermostats,door locks, etc.). An NMD is a networked computing device that typicallyincludes an arrangement of microphones, such as a microphone array, thatis configured to detect sound present in the NMD's environment. In someexamples, an NMD may be implemented within another device, such as anaudio playback device.

A voice input to such an NMD will typically include a wake word followedby an utterance comprising a user request. In practice, a wake word istypically a predetermined nonce word or phrase used to “wake up” an NMDand cause it to invoke a particular voice assistant service (“VAS”) tointerpret the intent of voice input in detected sound. For example, auser might speak the wake word “Alexa” to invoke the AMAZON® VAS, “Ok,Google” to invoke the GOOGLE® VAS, “Hey, Siri” to invoke the APPLE® VAS,or “Hey, Sonos” to invoke a VAS offered by SONOS®, among other examples.In practice, a wake word may also be referred to as, for example, anactivation-, trigger-, wakeup-word or -phrase, and may take the form ofany suitable word, combination of words (e.g., a particular phrase),and/or some other audio cue.

To identify whether sound detected by the NMD contains a voice inputthat includes a particular wake word, NMDs often utilize a wake-wordengine, which is typically onboard the NMD. The wake-word engine may beconfigured to identify (i.e., “spot” or “detect”) a particular wake wordin recorded audio using one or more identification algorithms. Suchidentification algorithms may include pattern recognition trained todetect the frequency and/or time domain patterns that speaking the wakeword creates. This wake-word identification process is commonly referredto as “keyword spotting.” In practice, to help facilitate keywordspotting, the NMD may buffer sound detected by a microphone of the NMDand then use the wake-word engine to process that buffered sound todetermine whether a wake word is present in the recorded audio.

When a wake-word engine detects a wake word in recorded audio, the NMDmay determine that a wake-word event (i.e., a “wake-word trigger”) hasoccurred, which indicates that the NMD has detected sound that includesa potential voice input. The occurrence of the wake-word event typicallycauses the NMD to perform additional processes involving the detectedsound. With a VAS wake-word engine, these additional processes mayinclude extracting detected-sound data from a buffer, among otherpossible additional processes, such as outputting an alert (e.g., anaudible chime and/or a light indicator) indicating that a wake word hasbeen identified. Extracting the detected sound may include reading outand packaging a stream of the detected-sound according to a particularformat and transmitting the packaged sound-data to an appropriate VASfor interpretation.

In turn, the VAS corresponding to the wake word that was identified bythe wake-word engine receives the transmitted sound data from the NMDover a communication network. A VAS traditionally takes the form of aremote service implemented using one or more cloud servers configured toprocess voice inputs (e.g., AMAZON's ALEXA, APPLE's SIRI, MICROSOFT'sCORTANA, GOOGLE'S ASSISTANT, etc.). In some instances, certaincomponents and functionality of the VAS may be distributed across localand remote devices.

When a VAS receives detected-sound data, the VAS processes this data,which involves identifying the voice input and determining intent ofwords captured in the voice input. The VAS may then provide a responseback to the NMD with some instruction according to the determinedintent. Based on that instruction, the NMD may cause one or more smartdevices to perform an action. For example, in accordance with aninstruction from a VAS, an NMD may cause a playback device to play aparticular song or an illumination device to turn on/off, among otherexamples. In some cases, an NMD, or a media system with NMDs (e.g., amedia playback system with NMD-equipped playback devices) may beconfigured to interact with multiple VASes. In practice, the NMD mayselect one VAS over another based on the particular wake word identifiedin the sound detected by the NMD.

In contrast to a predetermined nonce wake word that invokes a VAS, akeyword that invokes a command (referred to herein as a “commandkeyword”) may be a word or a combination of words (e.g., a phrase) thatfunctions as a command itself, such as a playback command. In someimplementations, a command keyword may function as both a wake word andthe command itself. That is, when a command-keyword engine detects acommand keyword in recorded audio, the NMD may determine that acommand-keyword event has occurred and responsively performs a commandcorresponding to the detected keyword. For instance, based on detectingthe command keyword “pause,” the NMD causes playback to be paused. Oneadvantage of a command-keyword engine is that the recorded audio doesnot necessarily need to be sent to a VAS for processing, which mayresult in a quicker response to the voice input as well as increaseduser privacy, among other possible benefits. In some implementationsdescribed below, a detected command-keyword event may cause one or moresubsequent actions, such as local natural language processing of a voiceinput. In some implementations, a command-keyword event may be onecondition among one or more other conditions that must be detectedbefore causing such actions. Additional command keyword implementationscan be found, for example, in U.S. patent application Ser. No.16/439,009, filed Jun. 12, 2019, titled “Network Microphone Device withCommand Keyword Conditioning”; U.S. patent application Ser. No.16/439,032, filed Jun. 12, 2019, titled “Network Microphone Device withCommand Word Eventing”; and U.S. patent application Ser. No. 16/439,046,filed Jun. 12, 2019, titled “Conditional Wake Word Eventing Based onEnvironment,” which are incorporated herein by reference in theirentireties.

According to example techniques described herein, after detecting acommand keyword, example NMDs may generate a command-keyword event (andperform a command corresponding to the detected command keyword) onlywhen certain conditions corresponding to the detected command keywordare met. For instance, after detecting the command keyword “skip,” anexample NMD generates a command-keyword event (and skips to the nexttrack) only when certain playback conditions indicating that a skipshould be performed are met. These playback conditions may include, forexample, (i) a first condition that a media item is being played back,(ii) a second condition that a queue is active, and (iii) a thirdcondition that the queue includes a media item subsequent to the mediaitem being played back. If any of these conditions are not satisfied,the command-keyword event is not generated (and no skip is performed).

In some instances, detection of a command keyword can be limited bycertain conditions. For example, if there is no content currently beingplayed back, the available intents to be identified by the local NLU canbe limited, for example by excluding keywords such as “pause,” “skip,”etc. Accordingly, while the media playback system is certain states, therange of potential keywords to be identified by the NLU can be limitedto decrease the rate of false positives.

By requiring both (a) detection of a command keyword and (b) certainconditions corresponding to the detected command keyword beforegenerating a command-keyword event, the prevalence of false positivesmay be reduced. For instance, when playing TV audio, dialogue or otherTV audio would not have the potential to generate false positives forthe “skip” command keyword since the TV audio input is active (and not aqueue). Moreover, the NMD can continually listen for command keywords(rather than requiring a button press to put the NMD in condition toreceive a voice input) as the conditions relating to the state of thecontrolled device gate command keyword event generation.

Aspects of conditioning keyword events may also be applicable to VASwake-word engines and other traditional nonce wake-word engines. Forexample, such conditioning can possibly make practicable other wake wordengines in addition to command-keyword engines that might otherwise beprone to false positives. For instance, an NMD may include a streamingaudio service wake word engine that supports certain wake words uniqueto the streaming audio service. For instance, after detecting astreaming audio service wake word, an example NMD generates a streamingaudio service wake word event only when certain streaming audio serviceplayback conditions are met. These playback conditions may include, forexample, (i) an active subscription to the streaming audio service and(ii) audio tracks from the streaming audio service in a queue, amongother examples.

Further, a command keyword may be a single word or a phrase. Phrasesgenerally include more syllables, which generally make the commandkeyword more unique and easier to identify by the command-keywordengine. Accordingly, in some cases, command keywords that are phrasesmay be less prone to false positive detections. Further, using a phrasemay allow more intent to be incorporated into the command keyword. Forinstance, a command keyword of “skip forward” signals that a skip shouldbe forward in a queue to a subsequent track, rather than backward to aprevious track.

Yet further, an NMD may include a local natural language unit (NLU). Asused herein, an NLU can be an onboard natural language understandingprocessor, or any other component or combination of componentsconfigured to recognize language in sound input data. In contrast to anNLU implemented in one or more cloud servers that is capable ofrecognizing a wide variety of voice inputs, example local NLUs arecapable of recognizing a relatively small library of keywords (e.g.,10,000 intents, words and/or phrases), which facilitates practicalimplementation on the NMD. When the command-keyword engine generates acommand-keyword event after detecting a command keyword in a voiceinput, the local NLU may process the voice input to look for keywordsfrom the library and determine an intent from the found keywords.

If the voice utterance portion of the voice input includes at least onekeyword from the library, the NMD may perform the command correspondingto the command keyword according to one or more parameters correspondingto the least one keyword. In other words, the keywords may alter orcustomize the command corresponding to the command keyword. Forinstance, the command-keyword engine may be configured to detect “play”as a command keyword and the local NLU library could include the phrase“low volume.” Then, if the user speaks “Play music at low volume” as avoice input, the command-keyword engine generates a command-keywordevent for “play” and uses the keyword “low volume” as a parameter forthe “play” command. Accordingly, the NMD not only causes playback basedon this voice input, but also lowers the volume. As another example, thecommand-keyword engine may be configured to detect “play” as a commandkeyword and the local NLU library could include the phrase “cancel.”Then, if the user speaks “Play music . . . never mind, cancel that” as avoice input, the command-keyword engine may generate a command-keywordevent for “play” but the keyword “cancel” is used as a parameter tomodify or nullify the “play” command such that no action is taken by theNMD in response to the voice input.

Example techniques involve customizing the keywords in the library tousers of the media playback system. For instance, the NMD may populatethe library using names (e.g., zone names, smart device names, and usernames) that have been configured in the media playback system. Yetfurther, the NMD may populate the local NLU library with names offavorite playlists, Internet radio stations, and the like. Suchcustomization allows the local NLU to more efficiently assist the userwith voice commands. Such customization may also be advantageous becausethe size of the local NLU library can be limited.

One possible advantage of a local NLU is increased privacy. Byprocessing voice input locally, a user may avoid transmitting voicerecordings to the cloud (e.g., to servers of a voice assistant service).Further, in some implementations, the NMD may use a local area networkto discover playback devices and/or smart devices connected to thenetwork, which may avoid providing this data to the cloud. Also, theuser's preferences and customizations may remain local to the NMD(s) inthe household, perhaps only using the cloud as an optional backup. Otheradvantages are possible as well.

Some environments (e.g., a user's household) can include multiple NMDs,each of which may include a command-keyword engine and/or a local NLU tofacilitate local processing of voice input. In these environments,keyword detection can be improved by leveraging the presence multipleNMDs in a number of ways. In some embodiments, results from differentNMDs can be compared to cross-check or confirm keyword detection.Additionally or alternatively, multiple NMDs can be used to expand thetotal library of supported keywords in the user's environment.

In some embodiments, different NMDs within a media playback system cansupport different libraries of keywords. As noted above, a local NLUassociated with an NMD may support a relatively limited library ofkeywords (e.g., approximately 10,000 intents, words and/or phrases) ascompared to its cloud-based counterparts. Accordingly, it can be usefulto increase the total available keywords in a media playback system byassigning different libraries of keywords to different NMDs within themedia playback system. For example, a first NMD might have a first NLUsupporting a first library of keywords, and a second NMD might have asecond NLU supporting a second, different library of keywords. As oneexample, if each NMD has a library with approximately 10,000 keywords,then two NMDs having completely non-overlapping libraries may provide acombined 20,000 keywords for the media playback system of which the twoNMDs are a part. In operation, voice input received at any one of theNMDs within the system can be processed for keyword detection amongmultiple NMDs. As such, a single voice input can be evaluated fordetection of keywords supported by two or more of the NMDs, therebysignificantly increasing the total library of keywords supported by thesystem.

In some embodiments, the different libraries can include dedicateddirectories. For example, a first NLU of a first NMD may include a firstlibrary of keywords that are associated with a first intent category(e.g., transport commands), while a second NLU of a second NMD includesa second library of keywords associated with a second intent category(e.g., Internet-of-Things (IOT) commands or media service providercommands). By supporting different directories, a voice input receivedvia a first NMD can be processed for detection of keywords associatedwith different intent categories, even if a single library on the firstNMD would be unable to store or support the keywords associated witheach of the different intent categories. In some embodiments, thededicated directories can include sets of keywords used most often onthose particular devices. For example, if, over time, a first NMDdetects the command “turn on lights in the living room” repeatedly,keywords associated with this request (e.g., “turn on lights” and“living room”) may be stored on the dedicated directory associated withthe first NMD. In some cases, those keywords may not be stored in thelibraries of other NMDs within the same media playback system.

In some embodiments, the different libraries supported by different NMDscan include partitions. For example, the library of a first NMD caninclude a first partition of shared keywords and a second partition ofdedicated keywords. The shared keywords may be separately stored on thelibraries of other NMDs within the same system, while the dedicatedkeywords may be stored only on that library, or in some instances onlyon a subset of all the libraries in the system. In some embodiments, theshared keywords can include keywords used most often (e.g., commontransport commands such as “pause,” “play,” etc.). By storing the mostcommonly used commands in libraries of each NMD, the system may moreconsistently and responsively detect these keywords and performassociated operations. In some embodiments, there may be multiplepartitions supported by each NMD, none of which is completely sharedwith other libraries. For example, the library of a first NMD mightinclude a first partition storing IOT-command keywords, and a secondpartition storing transport-control keywords, while the library of asecond NMD might include a first partition of user-associated keywords(e.g., the most command command-keywords associated with that user orenvironment) and a second partition storing keywords associated withmedia service providers.

Another way to improve local keyword detection via multiple NMDs is tocross-check keyword detection among two or more NMDs of the mediaplayback system. In one example, a first NMD may receive and processvoice input for keyword detection to obtain a result (e.g., a detectionof the word “pause” in input sound data). In parallel, a second NMD mayseparately process the voice input for keyword detection and transmitthe result back to the first NMD. The first NMD may then compare its ownresult with that obtained from the second NMD before determining whetherto perform a certain action. If, for example, the results match (e.g.,both NMDs identify the word “pause” in the voice input), the NMD mayperform an action corresponding to the keywords. If, in contrast, thedeterminations do not match (e.g., the first NMD identified the word“pause,” while the second NMD did not identify any keyword), then thefirst NMD may take no action, as this may indicate a lower confidence ineither result. In this way, a second NMD is leveraged to cross-check thedetermination made by the first NMD.

In some embodiments, the cross-check or confirmation determination canbe made not between two different NMDs, but between different subsets ofinput sound data from different microphones of a single NMD. Forexample, an NMD may have multiple microphones configured to generatesound data from a voice input. A first subset of the microphones may beused to generate first input sound data that can be evaluated toidentify a keyword. A second subset of the microphones may be used togenerate second input sound data from the same voice input that can beevaluated to identify a keyword. Comparing the results of these twoprocesses can increase confidence and reduce false positives.

As noted above, example techniques relate to locally distributed keyworddetection. A first example implementation involves a device including atleast one speaker, one or more microphones configured to detect sound, anetwork interface, one or more processors, and data storage havinginstructions stored thereon. The device receives input sound datarepresenting the sound detected by the one or more microphones anddetects, via a command-keyword engine, a first command keyword in afirst voice input represented in the input sound data. Thecommand-keyword engine is configured to (a) process input sound datarepresenting the sound detected by the at least one microphone and (b)generate a command-keyword event when the command-keyword enginedetects, in the input sound data, at least one of a plurality ofkeywords supported by the command-keyword engine. In response todetecting the first command keyword, the device makes a firstdetermination, via a first local natural language unit (NLU), whetherthe input sound data includes at least one keyword within a first afirst predetermined library of keywords from which the first NLU isconfigured to determine an intent of a given voice input. The devicereceives an indication of a second determination made by a second NLUthat the input sound data includes at least one keyword from thepredetermined library of keywords. The device compares the results ofthe first determination with the results of the second determinationand, based on the comparison, foregoes further processing of input sounddata. For example, the comparison may indicate that the twodeterminations do not match (e.g., they did not identify the samekeyword), and so no action is taken by the device.

A second example implementation involves a first device having at leastone speaker, one or more microphones configured to detect sound, anetwork interface, one or more processors, and data storage havinginstructions stored thereon. The first device receives input sound datarepresenting the sound detected by the one or more microphones anddetects, via a command-keyword engine, a first command keyword in afirst voice input represented in the input sound data. Thecommand-keyword engine is configured to (a) process input sound datarepresenting the sound detected by the at least one microphone and (b)generate a command-keyword event when the command-keyword enginedetects, in the input sound data, one of a plurality of keywordssupported by the command-keyword engine. In response to detecting thefirst command keyword, the first device determines, via a first localnatural language unit (NLU), whether the input sound data includes atleast one keyword within a first predetermined library of keywords fromwhich the first NLU is configured to determine an intent of a givenvoice input. The first device transmits, via the network interface overa local area network, the input sound data to a second device, thesecond device employing a second local NLU with a second predeterminedlibrary of keywords from which the second NLU is configured to determinean intent of a given voice input. The first device receives, via thenetwork interface, a response from the second device. After receivingthe response from the second device, the first device performs an actionbased on an intent determined by at least one of the first NLU or thesecond NLU according to the one or more particular keywords in the voiceinput.

While some embodiments described herein may refer to functions performedby given actors, such as “users” and/or other entities, it should beunderstood that this description is for purposes of explanation only.The claims should not be interpreted to require action by any suchexample actor unless explicitly required by the language of the claimsthemselves.

Moreover, some functions are described herein as being performed “basedon” or “in response to” another element or function. “Based on” shouldbe understood that one element or function is related to anotherfunction or element. “In response to” should be understood that oneelement or function is a necessary result of another function orelement. For the sake of brevity, functions are generally described asbeing based on another function when a functional link exists; however,such disclosure should be understood as disclosing either type offunctional relationship.

II. Example Operation Environment

FIGS. 1A and 1B illustrate an example configuration of a media playbacksystem 100 (or “MPS 100”) in which one or more embodiments disclosedherein may be implemented. Referring first to FIG. 1A, the MPS 100 asshown is associated with an example home environment having a pluralityof rooms and spaces, which may be collectively referred to as a “homeenvironment,” “smart home,” or “environment 101.” The environment 101comprises a household having several rooms, spaces, and/or playbackzones, including a master bathroom 101 a, a master bedroom 101 b,(referred to herein as “Nick's Room”), a second bedroom 101 c, a familyroom or den 101 d, an office 101 e, a living room 101 f, a dining room101 g, a kitchen 101 h, and an outdoor patio 10 i. While certainembodiments and examples are described below in the context of a homeenvironment, the technologies described herein may be implemented inother types of environments. In some embodiments, for example, the MPS100 can be implemented in one or more commercial settings (e.g., arestaurant, mall, airport, hotel, a retail or other store), one or morevehicles (e.g., a sports utility vehicle, bus, car, a ship, a boat, anairplane), multiple environments (e.g., a combination of home andvehicle environments), and/or another suitable environment wheremulti-zone audio may be desirable.

Within these rooms and spaces, the MPS 100 includes one or morecomputing devices. Referring to FIGS. 1A and 1B together, such computingdevices can include playback devices 102 (identified individually asplayback devices 102 a-102 o), network microphone devices 103(identified individually as “NMDs” 103 a-102 i), and controller devices104a and 104b (collectively “controller devices 104”). Referring to FIG.1B, the home environment may include additional and/or other computingdevices, including local network devices, such as one or more smartillumination devices 108 (FIG. 1B), a smart thermostat 110, and a localcomputing device 105 (FIG. 1A). In embodiments described below, one ormore of the various playback devices 102 may be configured as portableplayback devices, while others may be configured as stationary playbackdevices. For example, the headphones 102 o (FIG. 1B) are a portableplayback device, while the playback device 102 d on the bookcase may bea stationary device. As another example, the playback device 102 c onthe Patio may be a battery-powered device, which may allow it to betransported to various areas within the environment 101, and outside ofthe environment 101, when it is not plugged in to a wall outlet or thelike.

With reference still to FIG. 1B, the various playback, networkmicrophone, and controller devices 102, 103, and 104 and/or othernetwork devices of the MPS 100 may be coupled to one another viapoint-to-point connections and/or over other connections, which may bewired and/or wireless, via a network 111, such as a local area network(LAN) which may include a network router 109. As used herein, a localarea network can include any communications technology that is notconfigured for wide area communications, for example, WiFi, Bluetooth,Digital Enhanced Cordless Telecommunications (DECT), Ultra-WideBand,etc. For example, the playback device 102 j in the Den 101 d (FIG. 1A),which may be designated as the “Left” device, may have a point-to-pointconnection with the playback device 102 a, which is also in the Den 101d and may be designated as the “Right” device. In a related embodiment,the Left playback device 102 j may communicate with other networkdevices, such as the playback device 102 b, which may be designated asthe “Front” device, via a point-to-point connection and/or otherconnections via the NETWORK 111.

As further shown in FIG. 1B, the MPS 100 may be coupled to one or moreremote computing devices 106 via a wide area network (“WAN”) 107. Insome embodiments, each remote computing device 106 may take the form ofone or more cloud servers. The remote computing devices 106 may beconfigured to interact with computing devices in the environment 101 invarious ways. For example, the remote computing devices 106 may beconfigured to facilitate streaming and/or controlling playback of mediacontent, such as audio, in the home environment 101.

In some implementations, the various playback devices, NMDs, and/orcontroller devices 102-104 may be communicatively coupled to at leastone remote computing device associated with a VAS and at least oneremote computing device associated with a media content service (“MCS”).For instance, in the illustrated example of FIG. 1B, remote computingdevices 106 are associated with a VAS 190 and remote computing devices106 b are associated with an MCS 192. Although only a single VAS 190 anda single MCS 192 are shown in the example of FIG. 1B for purposes ofclarity, the MPS 100 may be coupled to multiple, different VASes and/orMCSes. In some implementations, VASes may be operated by one or more ofAMAZON, GOOGLE, APPLE, MICROSOFT, SONOS or other voice assistantproviders. In some implementations, MCSes may be operated by one or moreof SPOTIFY, PANDORA, AMAZON MUSIC, or other media content services.

As further shown in FIG. 1B, the remote computing devices 106 furtherinclude remote computing device 106 c configured to perform certainoperations, such as remotely facilitating media playback functions,managing device and system status information, directing communicationsbetween the devices of the MPS 100 and one or multiple VASes and/orMCSes, among other operations. In one example, the remote computingdevices 106 c provide cloud servers for one or more SONOS Wireless HiFiSystems.

In various implementations, one or more of the playback devices 102 maytake the form of or include an on-board (e.g., integrated) networkmicrophone device. For example, the playback devices 102 a-e include orare otherwise equipped with corresponding NMDs 103 a-e, respectively. Aplayback device that includes or is equipped with an NMD may be referredto herein interchangeably as a playback device or an NMD unlessindicated otherwise in the description. In some cases, one or more ofthe NMDs 103 may be a stand-alone device. For example, the NMDs 103 fand 103 g may be stand-alone devices. A stand-alone NMD may omitcomponents and/or functionality that is typically included in a playbackdevice, such as a speaker or related electronics. For instance, in suchcases, a stand-alone NMD may not produce audio output or may producelimited audio output (e.g., relatively low-quality audio output).

The various playback and network microphone devices 102 and 103 of theMPS 100 may each be associated with a unique name, which may be assignedto the respective devices by a user, such as during setup of one or moreof these devices. For instance, as shown in the illustrated example ofFIG. 1B, a user may assign the name “Bookcase” to playback device 102 dbecause it is physically situated on a bookcase. Similarly, the NMD 103f may be assigned the named “Island” because it is physically situatedon an island countertop in the Kitchen 101 h (FIG. 1A). Some playbackdevices may be assigned names according to a zone or room, such as theplayback devices 102 e, 102 l, 102 m, and 102 n, which are named“Bedroom,” “Dining Room,” “Living Room,” and “Office,” respectively.Further, certain playback devices may have functionally descriptivenames. For example, the playback devices 102 a and 102 b are assignedthe names “Right” and “Front,” respectively, because these two devicesare configured to provide specific audio channels during media playbackin the zone of the Den 101 d (FIG. 1A). The playback device 102 c in thePatio may be named portable because it is battery-powered and/or readilytransportable to different areas of the environment 101. Other namingconventions are possible.

As discussed above, an NMD may detect and process sound from itsenvironment, such as sound that includes background noise mixed withspeech spoken by a person in the NMD' s vicinity. For example, as soundsare detected by the NMD in the environment, the NMD may process thedetected sound to determine if the sound includes speech that containsvoice input intended for the NMD and ultimately a particular VAS. Forexample, the NMD may identify whether speech includes a wake wordassociated with a particular VAS.

In the illustrated example of FIG. 1B, the NMDs 103 are configured tointeract with the VAS 190 over a network via the network 111 and therouter 109. Interactions with the VAS 190 may be initiated, for example,when an NMD identifies in the detected sound a potential wake word. Theidentification causes a wake-word event, which in turn causes the NMD tobegin transmitting detected-sound data to the VAS 190. In someimplementations, the various local network devices 102-105 (FIG. 1A)and/or remote computing devices 106 c of the MPS 100 may exchangevarious feedback, information, instructions, and/or related data withthe remote computing devices associated with the selected VAS. Suchexchanges may be related to or independent of transmitted messagescontaining voice inputs. In some embodiments, the remote computingdevice(s) and the MPS 100 may exchange data via communication paths asdescribed herein and/or using a metadata exchange channel as describedin U.S. application Ser. No. 15/438,749 filed Feb. 21, 2017, and titled“Voice Control of a Media Playback System,” which is herein incorporatedby reference in its entirety.

Upon receiving the stream of sound data, the VAS 190 determines if thereis voice input in the streamed data from the NMD, and if so the VAS 190will also determine an underlying intent in the voice input. The VAS 190may next transmit a response back to the MPS 100, which can includetransmitting the response directly to the NMD that caused the wake-wordevent. The response is typically based on the intent that the VAS 190determined was present in the voice input. As an example, in response tothe VAS 190 receiving a voice input with an utterance to “Play Hey Judeby The Beatles,” the VAS 190 may determine that the underlying intent ofthe voice input is to initiate playback and further determine thatintent of the voice input is to play the particular song “Hey Jude.”After these determinations, the VAS 190 may transmit a command to aparticular MCS 192 to retrieve content (i.e., the song “Hey Jude”), andthat MCS 192, in turn, provides (e.g., streams) this content directly tothe MPS 100 or indirectly via the VAS 190. In some implementations, theVAS 190 may transmit to the MPS 100 a command that causes the MPS 100itself to retrieve the content from the MCS 192.

In certain implementations, NMDs may facilitate arbitration amongst oneanother when voice input is identified in speech detected by two or moreNMDs located within proximity of one another. For example, theNMD-equipped playback device 102 d in the environment 101 (FIG. 1A) isin relatively close proximity to the NMD-equipped Living Room playbackdevice 102 m, and both devices 102 d and 102 m may at least sometimesdetect the same sound. In such cases, this may require arbitration as towhich device is ultimately responsible for providing detected-sound datato the remote VAS. Examples of arbitrating between NMDs may be found,for example, in previously referenced U.S. application Ser. No.15/438,749. When performing local command-keyword detection, asdescribed in more detail below, it may be useful to forego or delay anysuch arbitration, such that two or more NMDs may process the same voiceinput for command-keyword detection. This can allow results of voiceprocessing of two or more different NMDS to be compared to one anotheras a way to cross-check keyword detection results. In some embodiments,results of NLU determinations associated with different NMDs can be usedto arbitrate between them. For example, if a first NLU associated with afirst NMD identifies a keyword with a higher confidence level than thatof a second NLU associated with the second NMD, then the first NMD maybe selected over the second NMD.

In certain implementations, an NMD may be assigned to, or otherwiseassociated with, a designated or default playback device that may notinclude an NMD. For example, the Island NMD 103 f in the Kitchen 101 h(FIG. 1A) may be assigned to the Dining Room playback device 102 l,which is in relatively close proximity to the Island NMD 103 f. Inpractice, an NMD may direct an assigned playback device to play audio inresponse to a remote VAS receiving a voice input from the NMD to playthe audio, which the NMD might have sent to the VAS in response to auser speaking a command to play a certain song, album, playlist, etc.Additional details regarding assigning NMDs and playback devices asdesignated or default devices may be found, for example, in previouslyreferenced U.S. patent application Ser. No.

Further aspects relating to the different components of the example MPS100 and how the different components may interact to provide a user witha media experience may be found in the following sections. Whilediscussions herein may generally refer to the example MPS 100,technologies described herein are not limited to applications within,among other things, the home environment described above. For instance,the technologies described herein may be useful in other homeenvironment configurations comprising more or fewer of any of theplayback, network microphone, and/or controller devices 102-104. Forexample, the technologies herein may be utilized within an environmenthaving a single playback device 102 and/or a single NMD 103. In someexamples of such cases, the NETWORK 111 (FIG. 1B) may be eliminated andthe single playback device 102 and/or the single NMD 103 may communicatedirectly with the remote computing devices 106-d. In some embodiments, atelecommunication network (e.g., an LTE network, a 5G network, etc.) maycommunicate with the various playback, network microphone, and/orcontroller devices 102-104 independent of a LAN.

a. Example Playback & Network Microphone Devices

FIG. 2A is a functional block diagram illustrating certain aspects ofone of the playback devices 102 of the MPS 100 of FIGS. 1A and 1B. Asshown, the playback device 102 includes various components, each ofwhich is discussed in further detail below, and the various componentsof the playback device 102 may be operably coupled to one another via asystem bus, communication network, or some other connection mechanism.In the illustrated example of FIG. 2A, the playback device 102 may bereferred to as an “NMD-equipped” playback device because it includescomponents that support the functionality of an NMD, such as one of theNMDs 103 shown in FIG. 1A.

As shown, the playback device 102 includes at least one processor 212,which may be a clock-driven computing component configured to processinput data according to instructions stored in memory 213. The memory213 may be a tangible, non-transitory, computer-readable mediumconfigured to store instructions that are executable by the processor212. For example, the memory 213 may be data storage that can be loadedwith software code 214 that is executable by the processor 212 toachieve certain functions.

In one example, these functions may involve the playback device 102retrieving audio data from an audio source, which may be anotherplayback device. In another example, the functions may involve theplayback device 102 sending audio data, detected-sound data (e.g.,corresponding to a voice input), and/or other information to anotherdevice on a network via at least one network interface 224. In yetanother example, the functions may involve the playback device 102causing one or more other playback devices to synchronously playbackaudio with the playback device 102. In yet a further example, thefunctions may involve the playback device 102 facilitating being pairedor otherwise bonded with one or more other playback devices to create amulti-channel audio environment. Numerous other example functions arepossible, some of which are discussed below.

As just mentioned, certain functions may involve the playback device 102synchronizing playback of audio content with one or more other playbackdevices. During synchronous playback, a listener may not perceivetime-delay differences between playback of the audio content by thesynchronized playback devices. U.S. Pat. No. 8,234,395 filed on Apr. 4,2004, and titled “System and method for synchronizing operations among aplurality of independently clocked digital data processing devices,”which is hereby incorporated by reference in its entirety, provides inmore detail some examples for audio playback synchronization amongplayback devices.

To facilitate audio playback, the playback device 102 includes audioprocessing components 216 that are generally configured to process audioprior to the playback device 102 rendering the audio. In this respect,the audio processing components 216 may include one or moredigital-to-analog converters (“DAC”), one or more audio preprocessingcomponents, one or more audio enhancement components, one or moredigital signal processors (“DSPs”), and so on. In some implementations,one or more of the audio processing components 216 may be a subcomponentof the processor 212. In operation, the audio processing components 216receive analog and/or digital audio and process and/or otherwiseintentionally alter the audio to produce audio signals for playback.

The produced audio signals may then be provided to one or more audioamplifiers 217 for amplification and playback through one or morespeakers 218 operably coupled to the amplifiers 217. The audioamplifiers 217 may include components configured to amplify audiosignals to a level for driving one or more of the speakers 218.

Each of the speakers 218 may include an individual transducer (e.g., a“driver”) or the speakers 218 may include a complete speaker systeminvolving an enclosure with one or more drivers. A particular driver ofa speaker 218 may include, for example, a subwoofer (e.g., for lowfrequencies), a mid-range driver (e.g., for middle frequencies), and/ora tweeter (e.g., for high frequencies). In some cases, a transducer maybe driven by an individual corresponding audio amplifier of the audioamplifiers 217. In some implementations, a playback device may notinclude the speakers 218, but instead may include a speaker interfacefor connecting the playback device to external speakers. In certainembodiments, a playback device may include neither the speakers 218 northe audio amplifiers 217, but instead may include an audio interface(not shown) for connecting the playback device to an external audioamplifier or audio-visual receiver.

In addition to producing audio signals for playback by the playbackdevice 102, the audio processing components 216 may be configured toprocess audio to be sent to one or more other playback devices, via thenetwork interface 224, for playback. In example scenarios, audio contentto be processed and/or played back by the playback device 102 may bereceived from an external source, such as via an audio line-in interface(e.g., an auto-detecting 3.5mm audio line-in connection) of the playbackdevice 102 (not shown) or via the network interface 224, as describedbelow.

As shown, the at least one network interface 224, may take the form ofone or more wireless interfaces 225 and/or one or more wired interfaces226. A wireless interface may provide network interface functions forthe playback device 102 to wirelessly communicate with other devices(e.g., other playback device(s), NMD(s), and/or controller device(s)) inaccordance with a communication protocol (e.g., any wireless standardincluding IEEE 802.11a, 802.11b, 802.11g 802.11n, 802.11ac, 802.15, 4Gmobile communication standard, and so on). A wired interface may providenetwork interface functions for the playback device 102 to communicateover a wired connection with other devices in accordance with acommunication protocol (e.g., IEEE 802.3). While the network interface224 shown in FIG. 2A include both wired and wireless interfaces, theplayback device 102 may in some implementations include only wirelessinterface(s) or only wired interface(s).

In general, the network interface 224 facilitates data flow between theplayback device 102 and one or more other devices on a data network. Forinstance, the playback device 102 may be configured to receive audiocontent over the data network from one or more other playback devices,network devices within a LAN, and/or audio content sources over a WAN,such as the Internet. In one example, the audio content and othersignals transmitted and received by the playback device 102 may betransmitted in the form of digital packet data comprising an InternetProtocol (IP)-based source address and IP-based destination addresses.In such a case, the network interface 224 may be configured to parse thedigital packet data such that the data destined for the playback device102 is properly received and processed by the playback device 102.

As shown in FIG. 2A, the playback device 102 also includes voiceprocessing components 220 that are operably coupled to one or moremicrophones 222. The microphones 222 are configured to detect sound(i.e., acoustic waves) in the environment of the playback device 102,which is then provided to the voice processing components 220. Morespecifically, each microphone 222 is configured to detect sound andconvert the sound into a digital or analog signal representative of thedetected sound, which can then cause the voice processing component 220to perform various functions based on the detected sound, as describedin greater detail below. In one implementation, the microphones 222 arearranged as an array of microphones (e.g., an array of six microphones).In some implementations, the playback device 102 includes more than sixmicrophones (e.g., eight microphones or twelve microphones) or fewerthan six microphones (e.g., four microphones, two microphones, or asingle microphones).

In operation, the voice-processing components 220 are generallyconfigured to detect and process sound received via the microphones 222,identify potential voice input in the detected sound, and extractdetected-sound data to enable a VAS, such as the VAS 190 (FIG. 1B), toprocess voice input identified in the detected-sound data. The voiceprocessing components 220 may include one or more analog-to-digitalconverters, an acoustic echo canceller (“AEC”), a spatial processor(e.g., one or more multi-channel Wiener filters, one or more otherfilters, and/or one or more beam former components), one or more buffers(e.g., one or more circular buffers), one or more wake-word engines, oneor more voice extractors, and/or one or more speech processingcomponents (e.g., components configured to recognize a voice of aparticular user or a particular set of users associated with ahousehold), among other example voice processing components. In exampleimplementations, the voice processing components 220 may include orotherwise take the form of one or more DSPs or one or more modules of aDSP. In this respect, certain voice processing components 220 may beconfigured with particular parameters (e.g., gain and/or spectralparameters) that may be modified or otherwise tuned to achieveparticular functions. In some implementations, one or more of the voiceprocessing components 220 may be a subcomponent of the processor 212.

As further shown in FIG. 2A, the playback device 102 also includes powercomponents 227. The power components 227 include at least an externalpower source interface 228, which may be coupled to a power source (notshown) via a power cable or the like that physically connects theplayback device 102 to an electrical outlet or some other external powersource. Other power components may include, for example, transformers,converters, and like components configured to format electrical power.

In some implementations, the power components 227 of the playback device102 may additionally include an internal power source 229 (e.g., one ormore batteries) configured to power the playback device 102 without aphysical connection to an external power source. When equipped with theinternal power source 229, the playback device 102 may operateindependent of an external power source. In some such implementations,the external power source interface 228 may be configured to facilitatecharging the internal power source 229. As discussed before, a playbackdevice comprising an internal power source may be referred to herein asa “portable playback device.” On the other hand, a playback device thatoperates using an external power source may be referred to herein as a“stationary playback device,” although such a device may in fact bemoved around a home or other environment.

The playback device 102 further includes a user interface 240 that mayfacilitate user interactions independent of or in conjunction with userinteractions facilitated by one or more of the controller devices 104.In various embodiments, the user interface 240 includes one or morephysical buttons and/or supports graphical interfaces provided on touchsensitive screen(s) and/or surface(s), among other possibilities, for auser to directly provide input. The user interface 240 may furtherinclude one or more of lights (e.g., LEDs) and the speakers to providevisual and/or audio feedback to a user.

As an illustrative example, FIG. 2B shows an example housing 230 of theplayback device 102 that includes a user interface in the form of acontrol area 232 at a top portion 234 of the housing 230. The controlarea 232 includes buttons 236 a-c for controlling audio playback, volumelevel, and other functions. The control area 232 also includes a button236 d for toggling the microphones 222 to either an on state or an offstate.

As further shown in FIG. 2B, the control area 232 is at least partiallysurrounded by apertures formed in the top portion 234 of the housing 230through which the microphones 222 (not visible in FIG. 2B) receive thesound in the environment of the playback device 102. The microphones 222may be arranged in various positions along and/or within the top portion234 or other areas of the housing 230 so as to detect sound from one ormore directions relative to the playback device 102.

By way of illustration, SONOS, Inc. presently offers (or has offered)for sale certain playback devices that may implement certain of theembodiments disclosed herein, including a “PLAY:1,” “PLAY:3,” “PLAY:5,”“PLAYBAR,” “CONNECT:AMP,” “PLAYBASE,” “BEAM,” “CONNECT,” and “SUB.” Anyother past, present, and/or future playback devices may additionally oralternatively be used to implement the playback devices of exampleembodiments disclosed herein. Additionally, it should be understood thata playback device is not limited to the examples illustrated in FIGS. 2Aor 2B or to the SONOS product offerings. For example, a playback devicemay include, or otherwise take the form of, a wired or wirelessheadphone set, which may operate as a part of the MPS 100 via a networkinterface or the like. In another example, a playback device may includeor interact with a docking station for personal mobile media playbackdevices. In yet another example, a playback device may be integral toanother device or component such as a television, a lighting fixture, orsome other device for indoor or outdoor use.

FIG. 2C is a diagram of an example voice input 280 that may be processedby an NMD or an NMD-equipped playback device. The voice input 280 mayinclude a keyword portion 280 a and an utterance portion 280 b. Thekeyword portion 280 a may include a wake word or a command keyword. Inthe case of a wake word, the keyword portion 280 a corresponds todetected sound that caused a command-keyword event. The utteranceportion 280 b corresponds to detected sound that potentially comprises auser request following the keyword portion 280 a. An utterance portion280 b can be processed to identify the presence of any words indetected-sound data by the NMD in response to the event caused by thekeyword portion 280 a. In various implementations, an underlying intentcan be determined based on the words in the utterance portion 280 b. Incertain implementations, an underlying intent can also be based or atleast partially based on certain words in the keyword portion 280 a,such as when keyword portion includes a command keyword. In any case,the words may correspond to one or more commands, as well as a certaincommand and certain keywords. A keyword in the voice utterance portion280 b may be, for example, a word identifying a particular device orgroup in the MPS 100. For instance, in the illustrated example, thekeywords in the voice utterance portion 280 b may be one or more wordsidentifying one or more zones in which the music is to be played, suchas the Living Room and the Dining Room (FIG. 1A). In some cases, theutterance portion 280 b may include additional information, such asdetected pauses (e.g., periods of non-speech) between words spoken by auser, as shown in FIG. 2C. The pauses may demarcate the locations ofseparate commands, keywords, or other information spoke by the userwithin the utterance portion 280 b.

Based on certain command criteria, the NMD and/or a remote VAS may takeactions as a result of identifying one or more commands in the voiceinput. Command criteria may be based on the inclusion of certainkeywords within the voice input, among other possibilities.Additionally, or alternatively, command criteria for commands mayinvolve identification of one or more control-state and/or zone-statevariables in conjunction with identification of one or more particularcommands. Control-state variables may include, for example, indicatorsidentifying a level of volume, a queue associated with one or moredevices, and playback state, such as whether devices are playing aqueue, paused, etc. Zone-state variables may include, for example,indicators identifying which, if any, zone players are grouped.

In some implementations, the MPS 100 is configured to temporarily reducethe volume of audio content that it is playing upon detecting a certainkeyword, such as a wake word, in the keyword portion 280 a. The MPS 100may restore the volume after processing the voice input 280. Such aprocess can be referred to as ducking, examples of which are disclosedin U.S. patent application Ser. No. 15/438,749, incorporated byreference herein in its entirety.

FIG. 2D shows an example sound specimen. In this example, the soundspecimen corresponds to the sound-data stream (e.g., one or more audioframes) associated with a spotted wake word or command keyword in thekeyword portion 280 a of FIG. 2A. As illustrated, the example soundspecimen comprises sound detected in an NMD's environment (i)immediately before a wake or command word was spoken, which may bereferred to as a pre-roll portion (between times to and ti), (ii) whilea wake or command word was spoken, which may be referred to as awake-meter portion (between times t₁ and t₂), and/or (iii) after thewake or command word was spoken, which may be referred to as a post-rollportion (between times t₂ and t₃). Other sound specimens are alsopossible. In various implementations, aspects of the sound specimen canbe evaluated according to an acoustic model which aims to mapmels/spectral features to phonemes in a given language model for furtherprocessing. For example, automatic speech recognition (ASR) may includesuch mapping for keyword detection. Wake-word detection engines, bycontrast, may be precisely tuned to identify a specific wake-word, and adownstream action of invoking a VAS (e.g., by targeting only nonce wordsin the voice input processed by the playback device).

ASR for command keyword detection may be tuned to accommodate a widerange of keywords (e.g., 5, 10, 100, 1,000, 10,000 keywords).Command-keyword detection, in contrast to wake-word detection, mayinvolve feeding ASR output to an onboard, local NLU which together withthe ASR determine when command-keyword events have occurred. In someimplementations described below, the local NLU may determine an intentbased on one or more other keywords in the ASR output produced by aparticular voice input. In these or other implementations, a playbackdevice may act on a detected command-keyword event only when theplayback devices determines that certain conditions have been met, suchas environmental conditions (e.g., low background noise). In someembodiments, multiple devices within a single media playback system mayhave different onboard, local ASRs and/or NLUs, for example supportingdifferent libraries of keywords.

b. Example Playback Device Configurations

FIGS. 3A-3E show example configurations of playback devices. Referringfirst to FIG. 3A, in some example instances, a single playback devicemay belong to a zone. For example, the playback device 102 c (FIG. 1A)on the Patio may belong to Zone A. In some implementations describedbelow, multiple playback devices may be “bonded” to form a “bondedpair,” which together form a single zone. For example, the playbackdevice 102 f (FIG. 1A) named “Bed 1” in FIG. 3A may be bonded to theplayback device 102 g (FIG. 1A) named “Bed 2” in FIG. 3A to form Zone B.Bonded playback devices may have different playback responsibilities(e.g., channel responsibilities). In another implementation describedbelow, multiple playback devices may be merged to form a single zone.For example, the playback device 102 d named “Bookcase” may be mergedwith the playback device 102 m named “Living Room” to form a single ZoneC. The merged playback devices 102 d and 102 m may not be specificallyassigned different playback responsibilities. That is, the mergedplayback devices 102 d and 102 m may, aside from playing audio contentin synchrony, each play audio content as they would if they were notmerged.

For purposes of control, each zone in the MPS 100 may be represented asa single user interface (“UI”) entity. For example, as displayed by thecontroller devices 104, Zone A may be provided as a single entity named“Portable,” Zone B may be provided as a single entity named “Stereo,”and Zone C may be provided as a single entity named “Living Room.”

In various embodiments, a zone may take on the name of one of theplayback devices belonging to the zone. For example, Zone C may take onthe name of the Living Room device 102 m (as shown). In another example,Zone C may instead take on the name of the Bookcase device 102 d. In afurther example, Zone C may take on a name that is some combination ofthe Bookcase device 102 d and Living Room device 102 m. The name that ischosen may be selected by a user via inputs at a controller device 104.In some embodiments, a zone may be given a name that is different thanthe device(s) belonging to the zone. For example, Zone B in FIG. 3A isnamed “Stereo” but none of the devices in Zone B have this name. In oneaspect, Zone B is a single UI entity representing a single device named“Stereo,” composed of constituent devices “Bed 1” and “Bed 2.” In oneimplementation, the Bed 1 device may be playback device 102 f in themaster bedroom 101 b (FIG. 1A) and the Bed 2 device may be the playbackdevice 102 g also in the master bedroom 101 h (FIG. 1A).

As noted above, playback devices that are bonded may have differentplayback responsibilities, such as playback responsibilities for certainaudio channels. For example, as shown in FIG. 3B, the Bed 1 and Bed 2devices 102 f and 102 g may be bonded so as to produce or enhance astereo effect of audio content. In this example, the Bed 1 playbackdevice 102 f may be configured to play a left channel audio component,while the Bed 2 playback device 102 g may be configured to play a rightchannel audio component. In some implementations, such stereo bondingmay be referred to as “pairing.”

Additionally, playback devices that are configured to be bonded may haveadditional and/or different respective speaker drivers. As shown in FIG.3C, the playback device 102 b named “Front” may be bonded with theplayback device 102 k named “SUB.” The Front device 102 b may render arange of mid to high frequencies, and the SUB device 102 k may renderlow frequencies as, for example, a subwoofer. When unbonded, the Frontdevice 102 b may be configured to render a full range of frequencies. Asanother example, FIG. 3D shows the Front and SUB devices 102 b and 102 kfurther bonded with Right and Left playback devices 102 a and 102 j,respectively. In some implementations, the Right and Left devices 102 aand 102 j may form surround or “satellite” channels of a home theatersystem. The bonded playback devices 102 a, 102 b, 102 j, and 102 k mayform a single Zone D (FIG. 3A).

In some implementations, playback devices may also be “merged.” Incontrast to certain bonded playback devices, playback devices that aremerged may not have assigned playback responsibilities, but may eachrender the full range of audio content that each respective playbackdevice is capable of. Nevertheless, merged devices may be represented asa single UI entity (i.e., a zone, as discussed above). For instance,FIG. 3E shows the playback devices 102 d and 102 m in the Living Roommerged, which would result in these devices being represented by thesingle UI entity of Zone C. In one embodiment, the playback devices 102d and 102 m may playback audio in synchrony, during which each outputsthe full range of audio content that each respective playback device 102d and 102 m is capable of rendering.

In some embodiments, a stand-alone NMD may be in a zone by itself. Forexample, the NMD 103h from FIG. 1A is named “Closet” and forms Zone I inFIG. 3A. An NMD may also be bonded or merged with another device so asto form a zone. For example, the NMD 103 f named “Island” may be bondedwith the playback device 102 i Kitchen, which together form Zone F,which is also named “Kitchen.” Additional details regarding assigningNMDs and playback devices as designated or default devices may be found,for example, in previously referenced U.S. patent application Ser. No.15/438,749. In some embodiments, a stand-alone NMD may not be assignedto a zone.

Zones of individual, bonded, and/or merged devices may be arranged toform a set of playback devices that playback audio in synchrony. Such aset of playback devices may be referred to as a “group,” “zone group,”“synchrony group,” or “playback group.” In response to inputs providedvia a controller device 104, playback devices may be dynamically groupedand ungrouped to form new or different groups that synchronously playback audio content. For example, referring to FIG. 3A, Zone A may begrouped with Zone B to form a zone group that includes the playbackdevices of the two zones. As another example, Zone A may be grouped withone or more other Zones C-I. The Zones A-I may be grouped and ungroupedin numerous ways. For example, three, four, five, or more (e.g., all) ofthe Zones A-I may be grouped. When grouped, the zones of individualand/or bonded playback devices may play back audio in synchrony with oneanother, as described in previously referenced U.S. Pat. No. 8,234,395.Grouped and bonded devices are example types of associations betweenportable and stationary playback devices that may be caused in responseto a trigger event, as discussed above and described in greater detailbelow.

In various implementations, the zones in an environment may be assigneda particular name, which may be the default name of a zone within a zonegroup or a combination of the names of the zones within a zone group,such as “Dining Room+Kitchen,” as shown in FIG. 3A. In some embodiments,a zone group may be given a unique name selected by a user, such as“Nick's Room,” as also shown in FIG. 3A. The name “Nick's Room” may be aname chosen by a user over a prior name for the zone group, such as theroom name “Master Bedroom.”

Referring back to FIG. 2A, certain data may be stored in the memory 213as one or more state variables that are periodically updated and used todescribe the state of a playback zone, the playback device(s), and/or azone group associated therewith. The memory 213 may also include thedata associated with the state of the other devices of the MPS 100,which may be shared from time to time among the devices so that one ormore of the devices have the most recent data associated with thesystem.

In some embodiments, the memory 213 of the playback device 102 may storeinstances of various variable types associated with the states.Variables instances may be stored with identifiers (e.g., tags)corresponding to type. For example, certain identifiers may be a firsttype “a1” to identify playback device(s) of a zone, a second type “b1”to identify playback device(s) that may be bonded in the zone, and athird type “c1” to identify a zone group to which the zone may belong.As a related example, in FIG. 1A, identifiers associated with the Patiomay indicate that the Patio is the only playback device of a particularzone and not in a zone group. Identifiers associated with the LivingRoom may indicate that the Living Room is not grouped with other zonesbut includes bonded playback devices 102 a, 102 b, 102 j, and 102 k.Identifiers associated with the Dining Room may indicate that the DiningRoom is part of Dining Room+Kitchen group and that devices 103 f and 102i are bonded. Identifiers associated with the Kitchen may indicate thesame or similar information by virtue of the Kitchen being part of theDining Room 30 Kitchen zone group. Other example zone variables andidentifiers are described below.

In yet another example, the MPS 100 may include variables or identifiersrepresenting other associations of zones and zone groups, such asidentifiers associated with Areas, as shown in FIG. 3A. An Area mayinvolve a cluster of zone groups and/or zones not within a zone group.For instance, FIG. 3A shows a first area named “First Area” and a secondarea named “Second Area.” The First Area includes zones and zone groupsof the Patio, Den, Dining Room, Kitchen, and Bathroom. The Second Areaincludes zones and zone groups of the Bathroom, Nick's Room, Bedroom,and Living Room. In one aspect, an Area may be used to invoke a clusterof zone groups and/or zones that share one or more zones and/or zonegroups of another cluster. In this respect, such an Area differs from azone group, which does not share a zone with another zone group. Furtherexamples of techniques for implementing Areas may be found, for example,in U.S. application Ser. No. 15/682,506 filed Aug. 21, 2017 and titled“Room Association Based on Name,” and U.S. Pat. No. 8,483,853 filed Sep.11, 2007, and titled “Controlling and manipulating groupings in amulti-zone media system.” Each of these applications is incorporatedherein by reference in its entirety. In some embodiments, the MPS 100may not implement Areas, in which case the system may not storevariables associated with Areas.

The memory 213 may be further configured to store other data. Such datamay pertain to audio sources accessible by the playback device 102 or aplayback queue that the playback device (or some other playbackdevice(s)) may be associated with. In embodiments described below, thememory 213 is configured to store a set of command data for selecting aparticular VAS when processing voice inputs. During operation, one ormore playback zones in the environment of FIG. 1A may each be playingdifferent audio content. For instance, the user may be grilling in thePatio zone and listening to hip hop music being played by the playbackdevice 102 c, while another user may be preparing food in the Kitchenzone and listening to classical music being played by the playbackdevice 102 i. In another example, a playback zone may play the sameaudio content in synchrony with another playback zone.

For instance, the user may be in the Office zone where the playbackdevice 102 n is playing the same hip-hop music that is being playing byplayback device 102 c in the Patio zone. In such a case, playbackdevices 102 c and 102 n may be playing the hip-hop in synchrony suchthat the user may seamlessly (or at least substantially seamlessly)enjoy the audio content that is being played out-loud while movingbetween different playback zones. Synchronization among playback zonesmay be achieved in a manner similar to that of synchronization amongplayback devices, as described in previously referenced U.S. Pat. No.8,234,395.

As suggested above, the zone configurations of the MPS 100 may bedynamically modified. As such, the MPS 100 may support numerousconfigurations. For example, if a user physically moves one or moreplayback devices to or from a zone, the MPS 100 may be reconfigured toaccommodate the change(s). For instance, if the user physically movesthe playback device 102 c from the Patio zone to the Office zone, theOffice zone may now include both the playback devices 102 c and 102 n.In some cases, the user may pair or group the moved playback device 102c with the Office zone and/or rename the players in the Office zoneusing, for example, one of the controller devices 104 and/or voiceinput. As another example, if one or more playback devices 102 are movedto a particular space in the home environment that is not already aplayback zone, the moved playback device(s) may be renamed or associatedwith a playback zone for the particular space.

Further, different playback zones of the MPS 100 may be dynamicallycombined into zone groups or split up into individual playback zones.For example, the Dining Room zone and the Kitchen zone may be combinedinto a zone group for a dinner party such that playback devices 102 iand 102 l may render audio content in synchrony. As another example,bonded playback devices in the Den zone may be split into (i) atelevision zone and (ii) a separate listening zone. The television zonemay include the Front playback device 102 b. The listening zone mayinclude the Right, Left, and SUB playback devices 102 a, 102 j, and 102k, which may be grouped, paired, or merged, as described above.Splitting the Den zone in such a manner may allow one user to listen tomusic in the listening zone in one area of the living room space, andanother user to watch the television in another area of the living roomspace. In a related example, a user may utilize either of the NMD 103 aor 103 b (FIG. 1B) to control the Den zone before it is separated intothe television zone and the listening zone. Once separated, thelistening zone may be controlled, for example, by a user in the vicinityof the NMD 103 a, and the television zone may be controlled, forexample, by a user in the vicinity of the NMD 103 b. As described above,however, any of the NMDs 103 may be configured to control the variousplayback and other devices of the MPS 100.

c. Example Controller Devices

FIG. 4 is a functional block diagram illustrating certain aspects of aselected one of the controller devices 104 of the MPS 100 of FIG. 1A.Such controller devices may also be referred to herein as a “controldevice” or “controller.” The controller device shown in FIG. 4 mayinclude components that are generally similar to certain components ofthe network devices described above, such as a processor 412, memory 413storing program software 414, at least one network interface 424, andone or more microphones 422. In one example, a controller device may bea dedicated controller for the MPS 100. In another example, a controllerdevice may be a network device on which media playback system controllerapplication software may be installed, such as for example, an iPhone™,iPad™ or any other smart phone, tablet, or network device (e.g., anetworked computer such as a PC or Mac™).

The memory 413 of the controller device 104 may be configured to storecontroller application software and other data associated with the MPS100 and/or a user of the system 100. The memory 413 may be loaded withinstructions in software 414 that are executable by the processor 412 toachieve certain functions, such as facilitating user access, control,and/or configuration of the MPS 100. The controller device 104 isconfigured to communicate with other network devices via the networkinterface 424, which may take the form of a wireless interface, asdescribed above.

In one example, system information (e.g., such as a state variable) maybe communicated between the controller device 104 and other devices viathe network interface 424. For instance, the controller device 104 mayreceive playback zone and zone group configurations in the MPS 100 froma playback device, an NMD, or another network device. Likewise, thecontroller device 104 may transmit such system information to a playbackdevice or another network device via the network interface 424. In somecases, the other network device may be another controller device.

The controller device 104 may also communicate playback device controlcommands, such as volume control and audio playback control, to aplayback device via the network interface 424. As suggested above,changes to configurations of the MPS 100 may also be performed by a userusing the controller device 104. The configuration changes may includeadding/removing one or more playback devices to/from a zone,adding/removing one or more zones to/from a zone group, forming a bondedor merged player, separating one or more playback devices from a bondedor merged player, among others.

As shown in FIG. 4, the controller device 104 also includes a userinterface 440 that is generally configured to facilitate user access andcontrol of the MPS 100. The user interface 440 may include atouch-screen display or other physical interface configured to providevarious graphical controller interfaces, such as the controllerinterfaces 540 a and 540 b shown in FIGS. 5A and 5B. Referring to FIGS.5A and 5B together, the controller interfaces 540 a and 540 b includes aplayback control region 542, a playback zone region 543, a playbackstatus region 544, a playback queue region 546, and a sources region548. The user interface as shown is just one example of an interfacethat may be provided on a network device, such as the controller deviceshown in FIG. 4, and accessed by users to control a media playbacksystem, such as the MPS 100. Other user interfaces of varying formats,styles, and interactive sequences may alternatively be implemented onone or more network devices to provide comparable control access to amedia playback system.

The playback control region 542 (FIG. 5A) may include selectable icons(e.g., by way of touch or by using a cursor) that, when selected, causeplayback devices in a selected playback zone or zone group to play orpause, fast forward, rewind, skip to next, skip to previous, enter/exitshuffle mode, enter/exit repeat mode, enter/exit cross fade mode, etc.The playback control region 542 may also include selectable icons that,when selected, modify equalization settings and/or playback volume,among other possibilities.

The playback zone region 543 (FIG. 5B) may include representations ofplayback zones within the MPS 100. The playback zones regions 543 mayalso include a representation of zone groups, such as the DiningRoom+Kitchen zone group, as shown.

In some embodiments, the graphical representations of playback zones maybe selectable to bring up additional selectable icons to manage orconfigure the playback zones in the MPS 100, such as a creation ofbonded zones, creation of zone groups, separation of zone groups, andrenaming of zone groups, among other possibilities.

For example, as shown, a “group” icon may be provided within each of thegraphical representations of playback zones. The “group” icon providedwithin a graphical representation of a particular zone may be selectableto bring up options to select one or more other zones in the MPS 100 tobe grouped with the particular zone. Once grouped, playback devices inthe zones that have been grouped with the particular zone will beconfigured to play audio content in synchrony with the playbackdevice(s) in the particular zone. Analogously, a “group” icon may beprovided within a graphical representation of a zone group. In thiscase, the “group” icon may be selectable to bring up options to deselectone or more zones in the zone group to be removed from the zone group.Other interactions and implementations for grouping and ungrouping zonesvia a user interface are also possible. The representations of playbackzones in the playback zone region 543 (FIG. 5B) may be dynamicallyupdated as playback zone or zone group configurations are modified.

The playback status region 544 (FIG. 5A) may include graphicalrepresentations of audio content that is presently being played,previously played, or scheduled to play next in the selected playbackzone or zone group. The selected playback zone or zone group may bevisually distinguished on a controller interface, such as within theplayback zone region 543 and/or the playback status region 544. Thegraphical representations may include track title, artist name, albumname, album year, track length, and/or other relevant information thatmay be useful for the user to know when controlling the MPS 100 via acontroller interface.

The playback queue region 546 may include graphical representations ofaudio content in a playback queue associated with the selected playbackzone or zone group. In some embodiments, each playback zone or zonegroup may be associated with a playback queue comprising informationcorresponding to zero or more audio items for playback by the playbackzone or zone group. For instance, each audio item in the playback queuemay comprise a uniform resource identifier (URI), a uniform resourcelocator (URL), or some other identifier that may be used by a playbackdevice in the playback zone or zone group to find and/or retrieve theaudio item from a local audio content source or a networked audiocontent source, which may then be played back by the playback device.

In one example, a playlist may be added to a playback queue, in whichcase information corresponding to each audio item in the playlist may beadded to the playback queue. In another example, audio items in aplayback queue may be saved as a playlist. In a further example, aplayback queue may be empty, or populated but “not in use” when theplayback zone or zone group is playing continuously streamed audiocontent, such as Internet radio that may continue to play untilotherwise stopped, rather than discrete audio items that have playbackdurations. In an alternative embodiment, a playback queue can includeInternet radio and/or other streaming audio content items and be “inuse” when the playback zone or zone group is playing those items. Otherexamples are also possible.

When playback zones or zone groups are “grouped” or “ungrouped,”playback queues associated with the affected playback zones or zonegroups may be cleared or re-associated. For example, if a first playbackzone including a first playback queue is grouped with a second playbackzone including a second playback queue, the established zone group mayhave an associated playback queue that is initially empty, that containsaudio items from the first playback queue (such as if the secondplayback zone was added to the first playback zone), that contains audioitems from the second playback queue (such as if the first playback zonewas added to the second playback zone), or a combination of audio itemsfrom both the first and second playback queues. Subsequently, if theestablished zone group is ungrouped, the resulting first playback zonemay be re-associated with the previous first playback queue or may beassociated with a new playback queue that is empty or contains audioitems from the playback queue associated with the established zone groupbefore the established zone group was ungrouped. Similarly, theresulting second playback zone may be re-associated with the previoussecond playback queue or may be associated with a new playback queuethat is empty or contains audio items from the playback queue associatedwith the established zone group before the established zone group wasungrouped. Other examples are also possible.

With reference still to FIGS. 5A and 5B, the graphical representationsof audio content in the playback queue region 646 (FIG. 5A) may includetrack titles, artist names, track lengths, and/or other relevantinformation associated with the audio content in the playback queue. Inone example, graphical representations of audio content may beselectable to bring up additional selectable icons to manage and/ormanipulate the playback queue and/or audio content represented in theplayback queue. For instance, a represented audio content may be removedfrom the playback queue, moved to a different position within theplayback queue, or selected to be played immediately, or after anycurrently playing audio content, among other possibilities. A playbackqueue associated with a playback zone or zone group may be stored in amemory on one or more playback devices in the playback zone or zonegroup, on a playback device that is not in the playback zone or zonegroup, and/or some other designated device. Playback of such a playbackqueue may involve one or more playback devices playing back media itemsof the queue, perhaps in sequential or random order.

The sources region 548 may include graphical representations ofselectable audio content sources and/or selectable voice assistantsassociated with a corresponding VAS. The VASes may be selectivelyassigned. In some examples, multiple VASes, such as AMAZON's Alexa,MICROSOFT's Cortana, etc., may be invokable by the same NMD. In someembodiments, a user may assign a VAS exclusively to one or more NMDs.For example, a user may assign a first VAS to one or both of theplayback devices 102 a and 102 b in the Living Room shown in FIG. 1A,and a second VAS to the NMD 103 f in the Kitchen. Other examples arepossible.

d. Example Audio Content Sources

The audio sources in the sources region 548 may be audio content sourcesfrom which audio content may be retrieved and played by the selectedplayback zone or zone group. One or more playback devices in a zone orzone group may be configured to retrieve for playback audio content(e.g., according to a corresponding URI or URL for the audio content)from a variety of available audio content sources. In one example, audiocontent may be retrieved by a playback device directly from acorresponding audio content source (e.g., via a line-in connection). Inanother example, audio content may be provided to a playback device overa network via one or more other playback devices or network devices. Asdescribed in greater detail below, in some embodiments, audio contentmay be provided by one or more media content services.

Example audio content sources may include a memory of one or moreplayback devices in a media playback system such as the MPS 100 of FIG.1, local music libraries on one or more network devices (e.g., acontroller device, a network-enabled personal computer, or anetworked-attached storage (“NAS”)), streaming audio services providingaudio content via the Internet (e.g., cloud-based music services), oraudio sources connected to the media playback system via a line-in inputconnection on a playback device or network device, among otherpossibilities.

In some embodiments, audio content sources may be added or removed froma media playback system such as the MPS 100 of FIG. 1A. In one example,an indexing of audio items may be performed whenever one or more audiocontent sources are added, removed, or updated. Indexing of audio itemsmay involve scanning for identifiable audio items in allfolders/directories shared over a network accessible by playback devicesin the media playback system and generating or updating an audio contentdatabase comprising metadata (e.g., title, artist, album, track length,among others) and other associated information, such as a URI or URL foreach identifiable audio item found. Other examples for managing andmaintaining audio content sources may also be possible.

FIG. 6 is a message flow diagram illustrating data exchanges betweendevices of the MPS 100. At step 650 a, the MPS 100 receives anindication of selected media content (e.g., one or more songs, albums,playlists, podcasts, videos, stations) via the control device 104. Theselected media content can comprise, for example, media items storedlocally on or more devices (e.g., the audio source 105 of FIG. 1C)connected to the media playback system and/or media items stored on oneor more media service servers (one or more of the remote computingdevices 106 of FIG. 1B). In response to receiving the indication of theselected media content, the control device 104 transmits a message 651 ato the playback device 102 (FIGS. 1A-1C) to add the selected mediacontent to a playback queue on the playback device 102.

At step 650 b, the playback device 102 receives the message 651 a andadds the selected media content to the playback queue for play back.

At step 650 c, the control device 104 receives input corresponding to acommand to play back the selected media content. In response toreceiving the input corresponding to the command to play back theselected media content, the control device 104 transmits a message 651 bto the playback device 102 causing the playback device 102 to play backthe selected media content. In response to receiving the message 651 b,the playback device 102 transmits a message 651 c to the computingdevice 106 requesting the selected media content. The computing device106, in response to receiving the message 651 c, transmits a message 651d comprising data (e.g., audio data, video data, a URL, a URI)corresponding to the requested media content.

At step 650 d, the playback device 102 receives the message 651 d withthe data corresponding to the requested media content and plays back theassociated media content.

At step 650 e, the playback device 102 optionally causes one or moreother devices to play back the selected media content. In one example,the playback device 102 is one of a bonded zone of two or more players(FIG. 1M). The playback device 102 can receive the selected mediacontent and transmit all or a portion of the media content to otherdevices in the bonded zone. In another example, the playback device 102is a coordinator of a group and is configured to transmit and receivetiming information from one or more other devices in the group. Theother one or more devices in the group can receive the selected mediacontent from the computing device 106, and begin playback of theselected media content in response to a message from the playback device102 such that all of the devices in the group play back the selectedmedia content in synchrony.

III. Example Command-Keyword Eventing

FIG. 7A is functional block diagram showing aspects of an NMD 703configured in accordance with embodiments of the disclosure. The NMD 703may be generally similar to the NMD 103 and include similar components.As described in more detail below, the NMD 703 (FIG. 7A) is configuredto handle certain voice inputs locally, without necessarily transmittingdata representing the voice input to a voice assistant service. However,the NMD 703 is also configured to process other voice inputs using avoice assistant service.

Referring to FIG. 7A, the NMD 703 includes voice capture components(“VCC”) 760, a VAS wake-word engine 770 a, and a voice extractor 773.The VAS wake-word engine 770 a and the voice extractor 773 are operablycoupled to the VCC 760. The NMD 703 further comprises a command-keywordengine 771 a operably coupled to the VCC 760.

The NMD 703 further includes microphones 720 and the at least onenetwork interface 724 as described above and may also include othercomponents, such as audio amplifiers, a user interface, etc., which arenot shown in FIG. 7A for purposes of clarity. The microphones 720 of theNMD 703 are configured to provide detected sound, S_(D), from theenvironment of the NMD 703 to the VCC 760. The detected sound S_(D) maytake the form of one or more analog or digital signals. In exampleimplementations, the detected sound S_(D) may be composed of a pluralitysignals associated with respective channels 762 that are fed to the VCC760.

Each channel 762 may correspond to a particular microphone 720. Forexample, an NMD having six microphones may have six correspondingchannels. Each channel of the detected sound S_(D) may bear certainsimilarities to the other channels but may differ in certain regards,which may be due to the position of the given channel's correspondingmicrophone relative to the microphones of other channels. For example,one or more of the channels of the detected sound S_(D) may have agreater signal to noise ratio (“SNR”) of speech to background noise thanother channels.

As further shown in FIG. 7A, the VCC 760 includes an AEC 763, a spatialprocessor 764, and one or more buffers 768. In operation, the AEC 763receives the detected sound S_(D) and filters or otherwise processes thesound to suppress echoes and/or to otherwise improve the quality of thedetected sound S_(D) . That processed sound may then be passed to thespatial processor 764.

The spatial processor 764 is typically configured to analyze thedetected sound S_(D) and identify certain characteristics, such as asound's amplitude (e.g., decibel level), frequency spectrum,directionality, etc. In one respect, the spatial processor 764 may helpfilter or suppress ambient noise in the detected sound S_(D) frompotential user speech based on similarities and differences in theconstituent channels 762 of the detected sound S_(D), as discussedabove. As one possibility, the spatial processor 764 may monitor metricsthat distinguish speech from other sounds. Such metrics can include, forexample, energy within the speech band relative to background noise andentropy within the speech band—a measure of spectral structure—which istypically lower in speech than in most common background noise. In someimplementations, the spatial processor 764 may be configured todetermine a speech presence probability, examples of such functionalityare disclosed in U.S. patent application Ser. No. 15/984,073, filed May18, 2018, titled “Linear Filtering for Noise-Suppressed SpeechDetection,” which is incorporated herein by reference in its entirety.

In operation, the one or more buffers 768—one or more of which may bepart of or separate from the memory 213 (FIG. 2A)—capture datacorresponding to the detected sound S_(D). More specifically, the one ormore buffers 768 capture detected-sound data that was processed by theupstream AEC 764 and spatial processor 764.

The network interface 724 may then provide this information to a remoteserver that may be associated with the MPS 100. In one aspect, theinformation stored in the additional buffer 769 does not reveal thecontent of any speech but instead is indicative of certain uniquefeatures of the detected sound itself. In a related aspect, theinformation may be communicated between computing devices, such as thevarious computing devices of the MPS 100, without necessarilyimplicating privacy concerns. In practice, the MPS 100 can use thisinformation to adapt and fine tune voice processing algorithms,including sensitivity tuning as discussed below. In some implementationsthe additional buffer may comprise or include functionality similar tolookback buffers disclosed, for example, in U.S. patent application Ser.No. 15/989,715, filed May 25, 2018, titled “Determining and Adapting toChanges in Microphone Performance of Playback Devices”; U.S. patentapplication No. Ser. 16/141,875, filed Sep. 25, 2018, titled “VoiceDetection Optimization Based on Selected Voice Assistant Service”; andU.S. patent application Ser. No. 16/138,111, filed Sep. 21, 2018, titled“Voice Detection Optimization Using Sound Metadata,” which areincorporated herein by reference in their entireties.

In any event, the detected-sound data forms a digital representation(i.e., sound-data stream), S_(DS), of the sound detected by themicrophones 720. In practice, the sound-data stream S_(DS) may take avariety of forms. As one possibility, the sound-data stream S_(DS) maybe composed of frames, each of which may include one or more soundsamples. The frames may be streamed (i.e., read out) from the one ormore buffers 768 for further processing by downstream components, suchas the VAS wake-word engines 770 and the voice extractor 773 of the NMD703.

In some implementations, at least one buffer 768 captures detected-sounddata utilizing a sliding window approach in which a given amount (i.e.,a given window) of the most recently captured detected-sound data isretained in the at least one buffer 768 while older detected sound datais overwritten when it falls outside of the window. For example, atleast one buffer 768 may temporarily retain 20 frames of a soundspecimen at given time, discard the oldest frame after an expirationtime, and then capture a new frame, which is added to the 19 priorframes of the sound specimen.

In practice, when the sound-data stream S_(DS) is composed of frames,the frames may take a variety of forms having a variety ofcharacteristics. As one possibility, the frames may take the form ofaudio frames that have a certain resolution (e.g., 16 bits ofresolution), which may be based on a sampling rate (e.g., 44,100 Hz).Additionally, or alternatively, the frames may include informationcorresponding to a given sound specimen that the frames define, such asmetadata that indicates frequency response, power input level, SNR,microphone channel identification, and/or other information of the givensound specimen, among other examples. Thus, in some embodiments, a framemay include a portion of sound (e.g., one or more samples of a givensound specimen) and metadata regarding the portion of sound. In otherembodiments, a frame may only include a portion of sound (e.g., one ormore samples of a given sound specimen) or metadata regarding a portionof sound.

In any case, downstream components of the NMD 703 may process thesound-data stream S_(DS). For instance, the VAS wake-word engines 770are configured to apply one or more identification algorithms to thesound-data stream S_(DS) (e.g., streamed sound frames) to spot potentialwake words in the detected-sound S_(D). This process may be referred toas automatic speech recognition. The VAS wake-word engine 770 a andcommand-keyword engine 771 a apply different identification algorithmscorresponding to their respective wake words, and further generatedifferent events based on detecting a wake word in the detected soundS_(D).

Example wake word detection algorithms accept audio as input and providean indication of whether a wake word is present in the audio. Manyfirst- and third-party wake word detection algorithms are known andcommercially available. For instance, operators of a voice service maymake their algorithm available for use in third-party devices.Alternatively, an algorithm may be trained to detect certain wake-words.

For instance, when the VAS wake-word engine 770 a detects a potentialVAS wake word, the VAS work-word engine 770 a provides an indication ofa “VAS wake-word event” (also referred to as a “VAS wake-word trigger”).In the illustrated example of FIG. 7A, the VAS wake word engine 770 aoutputs a signal, Svw, that indicates the occurrence of a VAS wake-wordevent to the voice extractor 773.

In multi-VAS implementations, the NMD 703 may include a VAS selector 774(shown in dashed lines) that is generally configured to directextraction by the voice extractor 773 and transmission of the sound-datastream S_(DS) to the appropriate VAS when a given wake-word isidentified by a particular wake-word engine (and a correspondingwake-word trigger), such as the VAS wake-word engine 770 a and at leastone additional VAS wake-word engine 770 b (shown in dashed lines). Insuch implementations, the NMD 703 may include multiple, different VASwake word engines and/or voice extractors, each supported by arespective VAS.

Similar to the discussion above, each VAS wake-word engine 770 may beconfigured to receive as input the sound-data stream S_(DS) from the oneor more buffers 768 and apply identification algorithms to cause awake-word trigger for the appropriate VAS. Thus, as one example, the VASwake-word engine 770 a may be configured to identify the wake word“Alexa” and cause the NMD 703 to invoke the AMAZON VAS when “Alexa” isspotted. As another example, the wake-word engine 770 b may beconfigured to identify the wake word “Ok, Google” and cause the NMD 520to invoke the GOOGLE VAS when “Ok, Google” is spotted. In single-VASimplementations, the VAS selector 774 may be omitted.

In response to the VAS wake-word event (e.g., in response to the signalSvw indicating the wake-word event), the voice extractor 773 isconfigured to receive and format (e.g., packetize) the sound-data streamS_(DS). For instance, the voice extractor 773 packetizes the frames ofthe sound-data stream S_(DS) into messages. The voice extractor 773transmits or streams these messages, Mv, that may contain voice input inreal time or near real time to a remote VAS via the network interface724.

The VAS is configured to process the sound-data stream S_(DS) containedin the messages Mv sent from the NMD 703. More specifically, the NMD 703is configured to identify a voice input 780 based on the sound-datastream S_(DS). As described in connection with FIG. 2C, the voice input780 may include a keyword portion and an utterance portion. The keywordportion corresponds to detected sound that caused a wake-word event, orleads to a command-keyword event when one or more certain conditions,such as certain playback conditions, are met. For instance, when thevoice input 780 includes a VAS wake word, the keyword portioncorresponds to detected sound that caused the wake-word engine 770 a tooutput the wake-word event signal SVW to the voice extractor 773. Theutterance portion in this case corresponds to detected sound thatpotentially comprises a user request following the keyword portion.

When a VAS wake-word event occurs, the VAS may first process the keywordportion within the sound data stream SDS to verify the presence of a VASwake word. In some instances, the VAS may determine that the keywordportion comprises a false wake word (e.g., the word “Election” when theword “Alexa” is the target VAS wake word). In such an occurrence, theVAS may send a response to the NMD 703 with an instruction for the NMD703 to cease extraction of sound data, which causes the voice extractor773 to cease further streaming of the detected-sound data to the VAS.The VAS wake-word engine 770 a may resume or continue monitoring soundspecimens until it spots another potential VAS wake word, leading toanother VAS wake-word event. In some implementations, the VAS does notprocess or receive the keyword portion but instead processes only theutterance portion.

In any case, the VAS processes the utterance portion to identify thepresence of any words in the detected-sound data and to determine anunderlying intent from these words. The words may correspond to one ormore commands, as well as certain keywords. The keyword may be, forexample, a word in the voice input identifying a particular device orgroup in the MPS 100. For instance, in the illustrated example, thekeyword may be one or more words identifying one or more zones in whichthe music is to be played, such as the Living Room and the Dining Room(FIG. 1A).

To determine the intent of the words, the VAS is typically incommunication with one or more databases associated with the VAS (notshown) and/or one or more databases (not shown) of the MPS 100. Suchdatabases may store various user data, analytics, catalogs, and otherinformation for natural language processing and/or other processing. Insome implementations, such databases may be updated for adaptivelearning and feedback for a neural network based on voice-inputprocessing. In some cases, the utterance portion may include additionalinformation, such as detected pauses (e.g., periods of non-speech)between words spoken by a user, as shown in FIG. 2C. The pauses maydemarcate the locations of separate commands, keywords, or otherinformation spoke by the user within the utterance portion.

After processing the voice input, the VAS may send a response to the MPS100 with an instruction to perform one or more actions based on anintent it determined from the voice input. For example, based on thevoice input, the VAS may direct the MPS 100 to initiate playback on oneor more of the playback devices 102, control one or more of theseplayback devices 102 (e.g., raise/lower volume, group/ungroup devices,etc.), or turn on/off certain smart devices, among other actions. Afterreceiving the response from the VAS, the wake-word engine 770 a of theNMD 703 may resume or continue to monitor the sound-data stream S_(DS1)until it spots another potential wake-word, as discussed above.

In general, the one or more identification algorithms that a particularVAS wake-word engine, such as the VAS wake-word engine 770 a, appliesare configured to analyze certain characteristics of the detected soundstream S_(DS) and compare those characteristics to correspondingcharacteristics of the particular VAS wake-word engine's one or moreparticular VAS wake words. For example, the wake-word engine 770 a mayapply one or more identification algorithms to spot temporal andspectral characteristics in the detected sound stream S_(DS) that matchthe temporal and spectral characteristics of the engine's one or morewake words, and thereby determine that the detected sound S_(D)comprises a voice input including a particular VAS wake word.

In some implementations, the one or more identification algorithms maybe third-party identification algorithms (i.e., developed by a companyother than the company that provides the NMD 703). For instance,operators of a voice service (e.g., AMAZON) may make their respectivealgorithms (e.g., identification algorithms corresponding to AMAZON'sALEXA) available for use in third-party devices (e.g., the NMDs 103),which are then trained to identify one or more wake words for theparticular voice assistant service. Additionally, or alternatively, theone or more identification algorithms may be first-party identificationalgorithms that are developed and trained to identify certain wake wordsthat are not necessarily particular to a given voice service. Otherpossibilities also exist.

As noted above, the NMD 703 also includes a command-keyword engine 771 ain parallel with the VAS wake-word engine 770 a. Like the VAS wake-wordengine 770 a, the command-keyword engine 771 a may apply one or moreidentification algorithms corresponding to one or more wake words. A“command-keyword event” is generated when a particular command keywordis identified in the detected sound S_(D). In contrast to the noncewords typically as utilized as VAS wake words, command keywords functionas both the activation word and the command itself. For instance,example command keywords may correspond to playback commands (e.g.,“play,” “pause,” “skip,” etc.) as well as control commands (“turn on”),among other examples. Under appropriate conditions, based on detectingone of these command keywords, the NMD 703 performs the correspondingcommand.

The command-keyword engine 771 a can employ an automatic speechrecognizer 772. The ASR 772 is configured to output phonetic or phonemicrepresentations, such as text corresponding to words, based on sound inthe sound-data stream S_(DS) to text. For instance, the ASR 772 maytranscribe spoken words represented in the sound-data stream S_(DS) toone or more strings representing the voice input 780 as text. Thecommand-keyword engine 771 can feed ASR output (labeled as S_(ASR)) to alocal natural language unit (NLU) 779 that identifies particularkeywords as being command keywords for invoking command-keyword events,as described below.

As noted above, in some example implementations, the NMD 703 isconfigured to perform natural language processing, which may be carriedout using an onboard natural language understanding processor, referredto herein as a natural language unit (NLU) 779. The local NLU 779 isconfigured to analyze text output of the ASR 772 of the command-keywordengine 771 a to spot (i.e., detect or identify) keywords in the voiceinput 780. In FIG. 7A, this output is illustrated as the signal S_(ASR).The local NLU 779 includes a library of keywords (i.e., words andphrases) corresponding to respective commands and/or parameters.

In one aspect, the library of the local NLU 779 includes commandkeywords. When the local NLU 779 identifies a command keyword in thesignal S_(ASR), the command-keyword engine 771 a generates acommand-keyword event and performs a command corresponding to thecommand keyword in the signal S_(ASR), assuming that one or moreconditions corresponding to that command keyword are satisfied.

Further, the library of the local NLU 779 may also include keywordscorresponding to parameters. The local NLU 779 may then determine anunderlying intent from the matched keywords in the voice input 780. Forinstance, if the local NLU matches the keywords “David Bowie” and“kitchen” in combination with a play command, the local NLU 779 maydetermine an intent of playing David Bowie in the Kitchen 101 h on theplayback device 102 i. In contrast to a processing of the voice input780 by a cloud-based VAS, local processing of the voice input 780 by thelocal NLU 779 may be relatively less sophisticated, as the NLU 779 doesnot have access to the relatively greater processing capabilities andlarger voice databases that a VAS generally has access to. As describedin greater detail below, in some implementations multiple NMDs of asingle media playback system may be equipped with different libraries oftheir respective local NLUs 779. Voice input captured via a first NMDmay be processed for detection of keywords stored in any one of thelibraries of the various NMDs of the media playback system. As a result,the presence of multiple NMDs can increase the total available keywordsfor local detection. In various embodiments, the libraries of the NMDscan be identical, partially overlapping, or completely non-overlapping.

In some examples, the local NLU 779 may determine an intent with one ormore slots, which correspond to respective keywords. For instance,referring back to the play David Bowie in the Kitchen example, whenprocessing the voice input, the local NLU 779 may determine that anintent is to play music (e.g., intent=playMusic), while a first slotincludes David Bowie as target content (e.g., slot1=DavidBowie) and asecond slot includes the Kitchen 101 h as the target playback device(e.g., s1ot2=kitchen). Here, the intent (to “playMusic”) is based on thecommand keyword and the slots are parameters modifying the intent to aparticular target content and playback device.

Within examples, the command-keyword engine 771 a outputs a signal thatindicates the occurrence of a command-keyword event to the local NLU779. In response to the command-keyword event (e.g., in response to thesignal indicating the command-keyword event), the local NLU 779 isconfigured to receive and process the signal S_(ASR). In particular, thelocal NLU 779 looks at the words within the signal S_(ASR) to findkeywords that match keywords in the library of the local NLU 779. Insome embodiments, the signal S_(ASR) can be transmitted from the NMD toanother NMD for processing via its local NLU. For example, the ASR 772of a first NMD may generate output signal S_(ASR) which can include, forexample, one or more strings representing a transcription of the voiceinput 780. This signal S_(ASR) may then be transmitted to the local NLUof a second, separate NMD for processing to identify an intent based onthe S_(ASR). In various embodiments, this transmission of the signalS_(ASR) to a second, separate NMD can be performed instead of or inparallel with passing the signal S_(ASR) to the local NLU 779 of thefirst NMD.

Some error in performing local automatic speech recognition is expected.Within examples, the ASR 772 may generate a confidence score whentranscribing spoken words to text, which indicates how closely thespoken words in the voice input 780 matches the sound patterns for thatword. In some implementations, generating a command-keyword event isbased on the confidence score for a given command keyword. For instance,the command-keyword engine 771 a may generate a command-keyword eventwhen the confidence score for a given sound exceeds a given thresholdvalue (e.g., 0.5 on a scale of 0-1, indicating that the given sound ismore likely than not the command keyword). Conversely, when theconfidence score for a given sound is at or below the given thresholdvalue, the command-keyword engine 771 a does not generate thecommand-keyword event.

Similarly, some error in performing keyword matching is expected. Withinexamples, the local NLU may generate a confidence score when determiningan intent, which indicates how closely the transcribed words in thesignal S_(ASR) match the corresponding keywords in the library of thelocal NLU. In some implementations, performing an operation according toa determined intent is based on the confidence score for keywordsmatched in the signal S_(ASR). For instance, the NMD 703 may perform anoperation according to a determined intent when the confidence score fora given sound exceeds a given threshold value (e.g., 0.5 on a scale of0-1, indicating that the given sound is more likely than not the commandkeyword). Conversely, when the confidence score for a given intent is ator below the given threshold value, the NMD 703 does not perform theoperation according to the determined intent.

In some embodiments, keyword matching can be performed via NLUs of twoor more different NMDs on a local network, and the results can becompared or otherwise combined to cross-check the results, therebyincreasing confidence and reducing the rate of false positives. Forexample, a first NMD may identify a keyword in voice input with a firstconfidence score. A second NMD may separately perform keyword detectionon the same voice input (either by separately capturing the same userspeech or by receiving sound input data from the first NMD transmittedover the local area network). The second NMD may transmit the results ofits keyword matching to the first NMD for comparison and evaluation. If,for example, the first and second NMD each identified the same keyword,a false positive is less likely. If, by contrast, the first and secondNMD each identified a different keyword (or if one did not identify akeyword at all), then a false positive is more likely, and the first NMDmay decline to take further action. In some embodiments, the identifiedkeywords and/or any associated confidence scores can be compared betweenthe two NMDs to make a final intent determination. In some embodiments,the respective NLUs of the first and second NMDs can be similarly oridentically configured (e.g., having the same libraries of keywords), oroptionally the NLUs can be configured differently (e.g., havingdifferent libraries of keywords). Although these examples are describedwith respect to two NMDs, this comparison can be extended to three,four, five, or more different NMDs.

In some embodiments, such cross-checking can be performed not betweentwo different NMDs, but between different sound data streams SDSobtained via a single NMD 703. For example, the NMD 703 can beconfigured to generate a first sound-data stream S_(DS) representingdata obtained from a first subset of the microphones 720, and togenerate a second sound-data stream S_(DS) representing data obtainedfrom a second subset of the microphones 720 that is different from thefirst. In an NMD having six microphones 720, the first sound-data streamS_(DS) may be generated using data from microphones 1-3, while thesecond sound-data stream S_(DS) may be generated using data frommicrophones 4-6. Optionally, in some embodiments the subsets of themicrophones can include some overlapping microphones—for example thefirst sound-data stream S_(DS) can include data from microphones 1-4 andthe second sound data stream can include data from microphones 3-6.Additionally, in some embodiments there may be three, four, five, ormore different sound-data streams S_(DS) generated using differentsubsets of microphones or other variations in processing of voice input.Optionally, in some instances a sound-data stream S_(DS) can includeinput from individual microphones of different NMDs, for examplecombining inputs from two microphones of a first NMD and two microphonesof a second NMD. However generated, these different sound-data streamsS_(DS) can then be separately evaluated by the command-keyword engine771 and the results can be compared or otherwise combined. For example,the NMD 703 may perform an action if and only if each of the local NLU779 identifies the same keyword(s) in each of the evaluated sound-datastreams S_(DS).

As noted above, in some implementations, a phrase may be used as acommand keyword, which provides additional syllables to match (or notmatch). For instance, the phrase “play me some music” has more syllablesthan “play,” which provides additional sound patterns to match to words.Accordingly, command keywords that are phrases may generally be lessprone to false wake word triggers.

As indicated above, the NMD 703 generates a command-keyword event (andperforms a command corresponding to the detected command keyword) onlywhen certain conditions corresponding to a detected command keyword aremet. These conditions are intended to lower the prevalence of falsepositive command-keyword events. For instance, after detecting thecommand keyword “skip,” the NMD 703 generates a command-keyword event(and skips to the next track) only when certain playback conditionsindicating that a skip should be performed are met. These playbackconditions may include, for example, (i) a first condition that a mediaitem is being played back, (ii) a second condition that a queue isactive, and (iii) a third condition that the queue includes a media itemsubsequent to the media item being played back. If any of theseconditions are not satisfied, the command-keyword event is not generated(and no skip is performed).

The NMD 703 includes the one or more state machine(s) 775 to facilitatedetermining whether the appropriate conditions are met. The statemachine 775 transitions between a first state and a second state basedon whether one or more conditions corresponding to the detected commandkeyword are met. In particular, for a given command keywordcorresponding to a particular command requiring one or more particularconditions, the state machine 775 transitions into a first state whenone or more particular conditions are satisfied and transitions into asecond state when at least one condition of the one or more particularconditions is not satisfied.

Within example implementations, the command conditions are based onstates indicated in state variables. As noted above, the devices of theMPS 100 may store state variables describing the state of the respectivedevice. For instance, the playback devices 102 may store state variablesindicating the state of the playback devices 102, such as the audiocontent currently playing (or paused), the volume levels, networkconnection status, and the like). These state variables are updated(e.g., periodically, or based on an event (i.e., when a state in a statevariable changes)) and the state variables further can be shared amongthe devices of the MPS 100, including the NMD 703.

Similarly, the NMD 703 may maintain these state variables (either byvirtue of being implemented in a playback device or as a stand-aloneNMD). The state machine 775 monitors the states indicated in these statevariables, and determines whether the states indicated in theappropriate state variables indicate that the command condition(s) aresatisfied. Based on these determinations, the state machine 775transitions between the first state and the second state, as describedabove.

In some implementations, the command-keyword engine 771 may be disabledunless certain conditions have been met via the state machines, and/orthe available keywords to be identified by the command-keyword enginecan be limited based on conditions as reflected via the state machines.As one example, the first state and the second state of the statemachine 775 may operate as enable/disable toggles to the command-keywordengine 771 a. In particular, while a state machine 775 corresponding toa particular command keyword is in the first state, the state machine775 enables the command-keyword engine 771 a of the particular commandkeyword. Conversely, while the state machine 775 corresponding to theparticular command keyword is in the second state, the state machine 775disables the command-keyword engine 771 a of the particular commandkeyword. Accordingly, the disabled command-keyword engine 771 a ceasesanalyzing the sound-data stream S_(DS). In such cases when at least onecommand condition is not satisfied, the NMD 703 may suppress generationof command-keyword event when the command-keyword engine 771 a detects acommand keyword. Suppressing generation may involve gating, blocking orotherwise preventing output from the command-keyword engine 771 a fromgenerating the command-keyword event. Alternatively, suppressinggeneration may involve the NMD 703 ceasing to feed the sound data streamS_(DS) to the ASR 772. Such suppression prevents a command correspondingto the detected command keyword from being performed when at least onecommand condition is not satisfied. In such embodiments, thecommand-keyword engine 771 a may continue analyzing the sound datastream SDS while the state machine 775 is in the first state, butcommand-keyword events are disabled.

Other example conditions may be based on the output of a voice activitydetector (“VAD”) 765. The VAD 765 is configured to detect the presence(or lack thereof) of voice activity in the sound-data stream S_(DS). Inparticular, the VAD 765 may analyze frames corresponding to the pre-rollportion of the voice input 780 (FIG. 2D) with one or more voicedetection algorithms to determine whether voice activity was present inthe environment in certain time windows prior to a keyword portion ofthe voice input 780.

The VAD 765 may utilize any suitable voice activity detectionalgorithms. Example voice detection algorithms involve determiningwhether a given frame includes one or more features or qualities thatcorrespond to voice activity, and further determining whether thosefeatures or qualities diverge from noise to a given extent (e.g., if avalue exceeds a threshold for a given frame). Some example voicedetection algorithms involve filtering or otherwise reducing noise inthe frames prior to identifying the features or qualities.

In some examples, the VAD 765 may determine whether voice activity ispresent in the environment based on one or more metrics. For example,the VAD 765 can be configured distinguish between frames that includevoice activity and frames that don't include voice activity. The framesthat the VAD determines have voice activity may be caused by speechregardless of whether it near- or far-field. In this example and others,the VAD 765 may determine a count of frames in the pre-roll portion ofthe voice input 780 that indicate voice activity. If this count exceedsa threshold percentage or number of frames, the VAD 765 may beconfigured to output a signal or set a state variable indicating thatvoice activity is present in the environment. Other metrics may be usedas well in addition to, or as an alternative to, such a count.

The presence of voice activity in an environment may indicate that avoice input is being directed to the NMD 73. Accordingly, when the VAD765 indicates that voice activity is not present in the environment(perhaps as indicated by a state variable set by the VAD 765) this maybe configured as one of the command conditions for the command keywords.When this condition is met (i.e., the VAD 765 indicates that voiceactivity is present in the environment), the state machine 775 willtransition to the first state to enable performing commands based oncommand keywords, so long as any other conditions for a particularcommand keyword are satisfied.

Further, in some implementations, the NMD 703 may include a noiseclassifier 766. The noise classifier 766 is configured to determinesound metadata (frequency response, signal levels, etc.) and identifysignatures in the sound metadata corresponding to various noise sources.The noise classifier 766 may include a neural network or othermathematical model configured to identify different types of noise indetected sound data or metadata. One classification of noise may bespeech (e.g., far-field speech). Another classification may be aspecific type of speech, such as background speech, and example of whichis described in greater detail with reference to FIG. 8. Backgroundspeech may be differentiated from other types of voice-like activity,such as more general voice activity (e.g., cadence, pauses, or othercharacteristics) of voice-like activity detected by the VAD 765.

For example, analyzing the sound metadata can include comparing one ormore features of the sound metadata with known noise reference values ora sample population data with known noise. For example, any features ofthe sound metadata such as signal levels, frequency response spectra,etc. can be compared with noise reference values or values collected andaveraged over a sample population. In some examples, analyzing the soundmetadata includes projecting the frequency response spectrum onto aneigenspace corresponding to aggregated frequency response spectra from apopulation of NMDs. Further, projecting the frequency response spectrumonto an eigenspace can be performed as a pre-processing step tofacilitate downstream classification.

In various embodiments, any number of different techniques forclassification of noise using the sound metadata can be used, forexample machine learning using decision trees, or Bayesian classifiers,neural networks, or any other classification techniques. Alternativelyor additionally, various clustering techniques may be used, for exampleK-Means clustering, mean-shift clustering, expectation-maximizationclustering, or any other suitable clustering technique. Techniques toclassify noise may include one or more techniques disclosed in U.S.application Ser. No. 16/227,308 filed Dec. 20, 2018, and titled“Optimization of Network Microphone Devices Using Noise Classification,”which is herein incorporated by reference in its entirety.

To illustrate, FIG. 8 shows a first plot 882 a and a second plot 882 b.The first plot 882 a and the second plot 882 b show analyzed soundmetadata associated with background speech. These signatures shown inthe plots are generated using principal component analysis (PCA).Collected data from a variety of NMDs provides an overall distributionof possible frequency response spectra. In general, principal componentanalysis can be used to find the orthogonal basis that describes thevariance in all the field data. This eigenspace is reflected in thecontours shown in the plots of FIG. 8. Each dot in the plot represents aknown noise value (e.g., a single frequency response spectrum from anNMD exposed to the noted noise source) that is projected onto theeigenspace. As seen in FIG. 8, these known noise values cluster togetherwhen projected onto the eigenspace. In this example, the FIG. 8 plotsare representative of a four-vector analysis, where each vectorcorresponds to a respective feature. The features collectively are asignature for background speech.

Referring back to FIG. 7A, in some implementations, the additionalbuffer 769 (shown in dashed lines) may store information (e.g., metadataor the like) regarding the detected sound S_(D) that was processed bythe upstream AEC 763 and spatial processor 764. This additional buffer769 may be referred to as a “sound metadata buffer.” Examples of suchsound metadata include: (1) frequency response data, (2) echo returnloss enhancement measures, (3) voice direction measures; (4) arbitrationstatistics; and/or (5) speech spectral data. In example implementations,the noise classifier 766 may analyze the sound metadata in the buffer769 to classify noise in the detected sound SD.

As noted above, one classification of sound may be background speech,such as speech indicative of far-field speech and/or speech indicativeof a conversation not involving the NMD 703. The noise classifier 766may output a signal and/or set a state variable indicating thatbackground speech is present in the environment. The presence of voiceactivity (i.e., speech) in the pre-roll portion of the voice input 780indicates that the voice input 780 might not be directed to the NMD 703,but instead be conversational speech within the environment. Forinstance, a household member might speak something like “our kids shouldhave a play date soon” without intending to direct the command keyword“play” to the NMD 703.

Further, when the noise classifier indicates that background speech ispresent is present in the environment, this condition may disable thecommand-keyword engine 771 a. In some implementations, the condition ofbackground speech being absent in the environment (perhaps as indicatedby a state variable set by the noise classifier 766) is configured asone of the command conditions for the command keywords. Accordingly, thestate machine 775 will not transition to the first state when the noiseclassifier 766 indicates that background speech is present in theenvironment.

Further, the noise classifier 766 may determine whether backgroundspeech is present in the environment based on one or more metrics. Forexample, the noise classifier 766 may determine a count of frames in thepre-roll portion of the voice input 780 that indicate background speech.If this count exceeds a threshold percentage or number of frames, thenoise classifier 766 may be configured to output the signal or set thestate variable indicating that background speech is present in theenvironment. Other metrics may be used as well in addition to, or as analternative to, such a count.

Within example implementations, the NMD 703 may support a plurality ofcommand keywords. To facilitate such support, the command-keyword engine771 a may implement multiple identification algorithms corresponding torespective command keywords. Alternatively, the NMD 703 may implementadditional command-keyword engines 771 b configured to identifyrespective command keywords. Yet further, the library of the local NLU779 may include a plurality of command keywords and be configured tosearch for text patterns corresponding to these command keywords in thesignal S_(ASR).

Further, command keywords may require different conditions. Forinstance, the conditions for “skip” may be different than the conditionsfor “play” as “skip” may require that the condition that a media item isbeing played back and play may require the opposite condition that amedia item is not being played back. To facilitate these respectiveconditions, the NMD 703 may implement respective state machines 775corresponding to each command keyword. Alternatively, the NMD 703 mayimplement a state machine 775 having respective states for each commandkeyword. Other examples are possible as well.

To illustrate exemplary state machine operation, FIG. 7B is a blockdiagram illustrating the state machine 775 for an example commandkeyword requiring one or more command conditions. At 777 a, the statemachine 775 remains in the first state 778 a while all the commandconditions are satisfied. While the state machine 775 remains in thefirst state 778 a (and all command conditions are met), the NMD 703 willgenerate a command-keyword event when the command keyword is detected bythe command-keyword engine 771 a.

At 777 b, the state machine 775 transitions into the second state 778 bwhen any command condition is not satisfied. At 777 c, the state machine775 remains in the second state 778 b while any command condition is notsatisfied. While the state machine 775 remains in the second state 778b, the NMD 703 will not act on the command-keyword event when thecommand keyword is detected by the command-keyword engine 771 a.

Referring back to FIG. 7A, in some examples, the one or more additionalcommand-keyword engines 771 b may include custom command-keywordengines. Cloud service providers, such as streaming audio services, mayprovide a custom keyword engine pre-configured with identificationalgorithms configured to spot service-specific command keywords. Theseservice-specific command keywords may include commands for customservice features and/or custom names used in accessing the service.

For instance, the NMD 703 may include a particular streaming audioservice (e.g., Apple Music) command-keyword engine 771 b. Thisparticular command-keyword engine 771 b may be configured to detectcommand keywords specific to the particular streaming audio service andgenerate streaming audio service wake word events. For instance, onecommand keyword may be “Friends Mix,” which corresponds to a command toplay back a custom playlist generated from playback histories of one ormore “friends” within the particular streaming audio service.

In some embodiments, different NMDs 703 of the same media playbacksystem 100 can have different additional custom command-keyword engines771 b. For example, a first NMD may include a custom command-keywordengine 771 b having an NLU configured with a library of keywordsconfigured for a particular streaming audio service (e.g., Apple Music)while a second NMD includes a custom-command keyword engine 771 b havingan NLU configured with a library of keywords configured to a differentstreaming audio service (e.g., Spotify). In operation, voice inputreceived at either NMD may be transmitted to the other NMD forprocessing, such that in combination the media playback system mayeffectively evaluate voice input for keywords with the benefit ofmultiple different custom command-keyword engines 771 b distributedamong multiple different NMDs 703.

A custom command-keyword engine 771 b may be relatively more prone tofalse wake words than the VAS wake-word engine 770 a, as generally theVAS wake-word engine 770 a is more sophisticated than a customcommand-keyword engine 771 b. To mitigate this, custom command keywordsmay require one or more conditions to be satisfied before generating acustom command-keyword event. Further, in some implementations, in aneffort to reduce the prevalence of false positives, multiple conditionsmay be imposed as a requirement to include a custom command-keywordengine 771 b in the NMD 703.

These custom command keyword conditions may include service-specificconditions. For instance, command keywords corresponding to premiumfeatures or playlists may require a subscription as a condition. Asanother example, custom command keywords corresponding to a particularstreaming audio service may require media items from that streamingaudio service in the playback queue. Other conditions are possible aswell.

To gate custom command-keyword engines based on the custom commandkeyword conditions, the NMD 703 may additional state machines 775corresponding to each custom command keyword. Alternatively, the NMD 703may implement a state machine 775 having respective states for eachcustom command keyword. Other examples are possible as well. Thesecustom command conditions may depend on the state variables maintainedby the devices within the MPS 100, and may also depend on statevariables or other data structures representing a state of a useraccount of a cloud service, such as a streaming audio service.

FIGS. 9A and 9B show a table 985 illustrating exemplary command keywordsand corresponding conditions. As shown in the Figures, example commandkeywords may include cognates having similar intent and requiringsimilar conditions. For instance, the “next” command keyword hascognates of “skip” and “forward,” each of which invokes a skip commandunder appropriate conditions. The conditions shown in the table 985 areillustrative; various implementations may use different conditions.

Referring back to FIG. 7A, in example embodiments, the VAS wake-wordengine 770 a and the command-keyword engine 771 a may take a variety offorms. For example, the VAS wake-word engine 770 a and thecommand-keyword engine 771 a may take the form of one or more modulesthat are stored in memory of the NMD 703 (e.g., the memory 112 b of FIG.1F). As another example, the VAS wake-word engine 770 a and thecommand-keyword engine 771 a may take the form of a general purposes orspecial-purpose processor, or modules thereof. In this respect, multiplewake word engines 770 and 771 may be part of the same component of theNMD 703 or each wake-word engine 770 and 771 may take the form of acomponent that is dedicated for the particular wake-word engine. Otherpossibilities also exist.

To further reduce false positives, the command-keyword engine 771 a mayutilize a relative low sensitivity compared with the VAS wake-wordengine 770 a. In practice, a wake-word engine may include a sensitivitylevel setting that is modifiable. The sensitivity level may define adegree of similarity between a word identified in the detected soundstream S_(DS1) and the wake-word engine's one or more particular wakewords that is considered to be a match (i.e., that triggers a VASwake-word or command-keyword event). In other words, the sensitivitylevel defines how closely, as one example, the spectral characteristicsin the detected sound stream S_(DS2) must match the spectralcharacteristics of the engine's one or more wake words to be a wake-wordtrigger.

In this respect, the sensitivity level generally controls how many falsepositives that the VAS wake-word engine 770 a and command-keyword engine771 a identifies. For example, if the VAS wake-word engine 770 a isconfigured to identify the wake-word “Alexa” with a relatively highsensitivity, then false wake words of “Election” or “Lexus” may causethe wake-word engine 770 a to flag the presence of the wake-word“Alexa.” In contrast, if the command-keyword engine 771 a is configuredwith a relatively low sensitivity, then the false wake words of “may” or“day” would not cause the command-keyword engine 771 a to flag thepresence of the command keyword “Play.”

In practice, a sensitivity level may take a variety of forms. In exampleimplementations, a sensitivity level takes the form of a confidencethreshold that defines a minimum confidence (i.e., probability) levelfor a wake-word engine that serves as a dividing line between triggeringor not triggering a wake-word event when the wake-word engine isanalyzing detected sound for its particular wake word. In this regard, ahigher sensitivity level corresponds to a lower confidence threshold(and more false positives), whereas a lower sensitivity levelcorresponds to a higher confidence threshold (and fewer falsepositives). For example, lowering a wake-word engine's confidencethreshold configures it to trigger a wake-word event when it identifieswords that have a lower likelihood that they are the actual particularwake word, whereas raising the confidence threshold configures theengine to trigger a wake-word event when it identifies words that have ahigher likelihood that they are the actual particular wake word. Withinexamples, a sensitivity level of the command-keyword engine 771 a may bebased on more or more confidence scores, such as the confidence score inspotting a command keyword and/or a confidence score in determining anintent. Other examples of sensitivity levels are also possible.

In example implementations, sensitivity level parameters (e.g., therange of sensitivities) for a particular wake-word engine can beupdated, which may occur in a variety of manners. As one possibility, aVAS or other third-party provider of a given wake-word engine mayprovide to the NMD 703 a wake-word engine update that modifies one ormore sensitivity level parameters for the given VAS wake-word engine 770a. By contrast, the sensitive level parameters of the command-keywordengine 771 a may be configured by the manufacturer of the NMD 703 or byanother cloud service (e.g., for a custom wake-word engine 771 b).

Notably, within certain examples, the NMD 703 foregoes sending any datarepresenting the detected sound S_(D) (e.g., the messages Mv) to a VASwhen processing a voice input 780 including a command keyword. Inimplementations including the local NLU 779, the NMD 703 can furtherprocess the voice utterance portion of the voice input 780 (in additionto the keyword word portion) without necessarily sending the voiceutterance portion of the voice input 780 to the VAS. Accordingly,speaking a voice input 780 (with a command keyword) to the NMD 703 mayprovide increased privacy relative to other NMDs that process all voiceinputs using a VAS.

As indicated above, the keywords in the library of the local NLU 779 cancorrespond to parameters. These parameters may define to perform thecommand corresponding to the detected command keyword. When keywords arerecognized in the voice input 780, the command corresponding to thedetected command keyword is performed according to parameterscorresponding to the detected keywords.

For instance, an example voice input 780 may be “play music at lowvolume” with “play” being the command keyword portion (corresponding toa playback command) and “music at low volume” being the voice utteranceportion. When analyzing this voice input 780, the NLU 779 may recognizethat “low volume” is a keyword in its library corresponding to aparameter representing a certain (low) volume level. Accordingly, theNLU 779 may determine an intent to play at this lower volume level.Then, when performing the playback command corresponding to “play,” thiscommand is performed according to the parameter representing a certainvolume level.

In a second example, another example voice input 780 may be “play myfavorites in the Kitchen” with “play” again being the command keywordportion (corresponding to a playback command) and “my favorites in theKitchen” as the voice utterance portion. When analyzing this voice input780, the NLU 779 may recognize that “favorites” and “Kitchen” matchkeywords in its library. In particular, “favorites” corresponds to afirst parameter representing particular audio content (i.e., aparticular playlist that includes a user's favorite audio tracks) while“Kitchen” corresponds to a second parameter representing a target forthe playback command (i.e., the kitchen 101 h zone. Accordingly, the NLU779 may determine an intent to play this particular playlist in thekitchen 101 h zone.

In a third example, a further example voice input 780 may be “volume up”with “volume” being the command keyword portion (corresponding to avolume adjustment command) and “up” being the voice utterance portion.When analyzing this voice input 780, the NLU 779 may recognize that “up”is a keyword in its library corresponding to a parameter representing acertain volume increase (e.g., a 10-point increase on a 100-point volumescale). Accordingly, the NLU 779 may determine an intent to increasevolume. Then, when performing the volume adjustment commandcorresponding to “volume,” this command is performed according to theparameter representing the certain volume increase.

Within examples, certain command keywords are functionally linked to asubset of the keywords within the library of the local NLU 779, whichmay hasten analysis. For instance, the command keyword “skip” may befunctionality linked to the keywords “forward” and “backward” and theircognates. Accordingly, when the command keyword “skip” is detected in agiven voice input 780, analyzing the voice utterance portion of thatvoice input 780 with the local NLU 779 may involve determining whetherthe voice input 780 includes any keywords that match these functionallylinked keywords (rather than determining whether the voice input 780includes any keywords that match any keyword in the library of the localNLU 779). Since vastly fewer keywords are checked, this analysis isrelatively quicker than a full search of the library. By contrast, anonce VAS wake word such as “Alexa” provides no indication as to thescope of the accompanying voice input.

Some commands may require one or more parameters, as such the commandkeyword alone does not provide enough information to perform thecorresponding command. For example, the command keyword “volume” mightrequire a parameter to specify a volume increase or decrease, as theintent of “volume” of volume alone is unclear. As another example, thecommand keyword “group” may require two or more parameters identifyingthe target devices to group.

Accordingly, in some example implementations, when a given commandkeyword is detected in the voice input 780 by the command-keyword engine771 a, the local NLU 779 may determine whether the voice input 780includes keywords matching keywords in the library corresponding to therequired parameters. If the voice input 780 does include keywordsmatching the required parameters, the NMD 703 proceeds to perform thecommand (corresponding to the given command keyword) according to theparameters specified by the keywords.

However, if the voice input 780 does include keywords matching therequired parameters for the command, the NMD 703 may prompt the user toprovide the parameters. For instance, in a first example, the NMD 703may play an audible prompt such as “I've heard a command, but I needmore information” or “Can I help you with something?” Alternatively, theNMD 703 may send a prompt to a user's personal device via a controlapplication (e.g., the software components 132 c of the controldevice(s) 104).

In further examples, the NMD 703 may play an audible prompt customizedto the detected command keyword. For instance, after detecting a commandkeyword corresponding to a volume adjustment command (e.g., “volume”),the audible prompt may include a more specific request such as “Do youwant to adjust the volume up or down?” As another example, for agrouping command corresponding to the command keyword “group,” theaudible prompt may be “Which devices do you want to group?” Supportingsuch specific audible prompts may be made practicable by supporting arelatively limited number of command keywords (e.g., less than 100), butother implementations may support more command keywords with thetrade-off of requiring additional memory and processing capability.

Within additional examples, when a voice utterance portion does notinclude keywords corresponding to one or more required parameters, theNMD 703 may perform the corresponding command according to one or moredefault parameters. For instance, if a playback command does not includekeywords indicating target playback devices 102 for playback, the NMD703 may default to playback on the NMD 703 itself (e.g., if the NMD 703is implemented within a playback device 102) or to playback on one ormore associated playback devices 102 (e.g., playback devices 102 in thesame room or zone as the NMD 703). Further, in some examples, the usermay configure default parameters using a graphical user interface (e.g.,user interface 430) or voice user interface. For example, if a groupingcommand does not specify the playback devices 102 to group, the NMD 703may default to instructing two or more pre-configured default playbackdevices 102 to form a synchrony group. Default parameters may be storedin data storage (e.g., the memory 112 b (FIG. 1F)) and accessed when theNMD 703 determines that keywords exclude certain parameters. Otherexamples are possible as well.

In some cases, the NMD 703 sends the voice input 780 to a VAS when thelocal NLU 779 is unable to process the voice input 780 (e.g., when thelocal NLU is unable to find matches to keywords in the library, or whenthe local NLU 779 has a low confidence score as to intent). In anexample, to trigger sending the voice input 780, the NMD 703 maygenerate a bridging event, which causes the voice extractor 773 toprocess the sound-data stream SD, as discussed above. That is, the NMD703 generates a bridging event to trigger the voice extractor 773without a VAS wake-word being detected by the VAS wake word engine 770 a(instead based on a command keyword in the voice input 780, as well asthe NLU 779 being unable to process the voice input 780).

Before sending the voice input 780 to the VAS (e.g., via the messagesM_(V)), the NMD 703 may obtain confirmation from the user that the useracquiesces to the voice input 780 being sent to the VAS. For instance,the NMD 703 may play an audible prompt to send the voice input to adefault or otherwise configured VAS, such as “I'm sorry, I didn'tunderstand that. May I ask Alexa?” In another example, the NMD 703 mayplay an audible prompt using a VAS voice (i.e., a voice that is known tomost users as being associated with a particular VAS), such as “Can Ihelp you with something?” In such examples, generation of the bridgingevent (and trigging of the voice extractor 773) is contingent on asecond affirmative voice input 780 from the user.

Within certain example implementations, the local NLU 779 may processthe signal S_(ASR) without necessarily a command-keyword event beinggenerated by the command-keyword engine 771 a (i.e., directly). That is,the automatic speech recognition 772 may be configured to performautomatic speech recognition on the sound-data stream S_(D), which thelocal NLU 779 processes for matching keywords without requiring acommand-keyword event. If keywords in the voice input 780 are found tomatch keywords corresponding to a command (possibly with one or morekeywords corresponding to one or more parameters), the NMD 703 performsthe command according to the one or more parameters.

Further, in such examples, the local NLU 779 may process the signalS_(ASR) directly only when certain conditions are met. In particular, insome embodiments, the local NLU 779 processes the signal S_(ASR) onlywhen the state machine 775 is in the first state. The certain conditionsmay include a condition corresponding to no background speech in theenvironment. An indication of whether background speech is present inthe environment may come from the noise classifier 766. As noted above,the noise classifier 766 may be configured to output a signal or set astate variable indicating that far-field speech is present in theenvironment. Further, another condition may correspond to voice activityin the environment. The VAD 765 may be configured to output a signal orset a state variable indicating that voice activity is present in theenvironment. Similarly, the prevalence of false positive detection ofcommands with a direct processing approach may be mitigated using theconditions determined by the state machine 775.

In some examples, the library of the local NLU 779 is partiallycustomized to the individual user(s). In a first aspect, the library maybe customized to the devices that are within the household of the NMD(e.g., the household within the environment 101 (FIG. 1A)). Forinstance, the library of the local NLU may include keywordscorresponding to the names of the devices within the household, such asthe zone names of the playback devices 102 in the MPS 100. In a secondaspect, the library may be customized to the users of the devices withinthe household. For example, the library of the local NLU 779 may includekeywords corresponding to names or other identifiers of a user'spreferred playlists, artists, albums, and the like. Then, the user mayrefer to these names or identifiers when directing voice inputs to thecommand-keyword engine 771 a and the local NLU 779. In some embodiments,different NMDs 703 of the same media playback system 100 can havedifferent NLUs 779 with different customized libraries. For example, afirst NMD may include a first subset of device and zone names, and asecond NMD may include a second subset of device and zone names.

Within example implementations, the NMD 703 may populate the library ofthe local NLU 779 locally within the network 111 (FIG. 1B). As notedabove, the NMD 703 may maintain or have access to state variablesindicating the respective states of devices connected to the network 111(e.g., the playback devices 104). These state variables may includenames of the various devices. For instance, the kitchen 101 h mayinclude the playback device 102 b, which are assigned the zone name“Kitchen.” The NMD 703 may read these names from the state variables andinclude them in the library of the local NLU 779 by training the localNLU 779 to recognize them as keywords. The keyword entry for a givenname may then be associated with the corresponding device in anassociated parameter (e.g., by an identifier of the device, such as aMAC address or IP address). The NMD 703 can then use the parameters tocustomize control commands and direct the commands to a particulardevice.

In further examples, the NMD 703 may populate the library by discoveringdevices connected to the network 111. For instance, the NMD 703 maytransmit discovery requests via the network 111 according to a protocolconfigured for device discovery, such as universal plug-and-play (UPnP)or zero-configuration networking. Devices on the network 111 may thenrespond to the discovery requests and exchange data representing thedevice names, identifiers, addresses and the like to facilitatecommunication and control via the network 111. The NMD 703 may readthese names from the exchanged messages and include them in the libraryof the local NLU 779 by training the local NLU 779 to recognize them askeywords.

In further examples, the NMD 703 may populate the library using thecloud. To illustrate, FIG. 10 is a schematic diagram of the MPS 100 anda cloud network 902. The cloud network 902 includes cloud servers 906,identified separately as media playback system control servers 906 a,streaming audio service servers 906 b, and IOT cloud servers 906 c. Thestreaming audio service servers 906 b may represent cloud servers ofdifferent streaming audio services. Similarly, the IOT cloud servers 906c may represent cloud servers corresponding to different cloud servicessupporting smart devices 990 in the MPS 100.

One or more communication links 903 a, 903 b, and 903 c (referred tohereinafter as “the links 903”) communicatively couple the MPS 100 andthe cloud servers 906. The links 903 can include one or more wirednetworks and one or more wireless networks (e.g., the Internet).Further, similar to the network 111 (FIG. 1B), a network 911communicatively couples the links 903 and at least a portion of thedevices (e.g., one or more of the playback devices 102, NMDs 103 and703, control devices 104, and/or smart devices 990) of the MPS 100.

In some implementations, the media playback system control servers 906 afacilitate populating the library of local NLU 779 with the NMD(s) 703(representing one or more of the NMD 703 (FIG. 7A) within the MPS 100).In an example, the media playback system control servers 906 a mayreceive data representing a request to populate the library of a localNLU 779 from the NMD 703. Based on this request, the media playbacksystem control servers 906 a may communicate with the streaming audioservice servers 906 b and/or IOT cloud servers 906 c to obtain keywordsspecific to the user.

In some embodiments, different NMDs 703 of the same media playbacksystem 100 can have different NLUs 779 with different customizedlibraries. For example, a first NMD may have an NLU 779 with a libraryof keywords associated with IOT commands while a second NMD may have anNLU 779 with a library of keywords associated with media streamingservices commands. In some embodiments, the library of an NLU 779 caninclude two or more partitions having different sets of keywords. Forexample, an NLU 779 can include a first partition of keywords associatedwith transport commands, and a second partition of keywords associatedwith IOT commands. One or more of such partitions can be populated usingthe cloud as described above. For example, the NLU 779 can have an IOTpartition in its library that contains keywords populated by one or moreof the IOT cloud servers 906 c, while a different NLU can have a mediastreaming service partition in its library that contains keywordspopulated by one or more of the audio service servers 906 b.

In some examples, the media playback system control servers 906 a mayutilize user accounts and/or user profiles in obtaining keywordsspecific to the user. As noted above, a user of the MPS 100 may set-up auser profile to define settings and other information within the MPS100. The user profile may then in turn be registered with user accountsof one or more streaming audio services to facilitate streaming audiofrom such services to the playback devices 102 of the MPS 100.

Through use of these registered streaming audio services, the streamingaudio service servers 906 b may collect data indicating a user's savedor preferred playlists, artists, albums, tracks, and the like, eithervia usage history or via user input (e.g., via a user input designatinga media item as saved or a favorite). This data may be stored in adatabase on the streaming audio service servers 906 b to facilitateproviding certain features of the streaming audio service to the user,such as custom playlists, recommendations, and similar features. Underappropriate conditions (e.g., after receiving user permission), thestreaming audio service servers 906 b may share this data with the mediaplayback system control servers 906 a over the links 903 b.

Accordingly, within examples, the media playback system control servers906 a may maintain or have access to data indicating a user's saved orpreferred playlists, artists, albums, tracks, genres, and the like. If auser has registered their user profile with multiple streaming audioservices, the saved data may include saved playlists, artists, albums,tracks, and the like from two or more streaming audio services. Further,the media playback system control servers 906 a may develop a morecomplete understanding of the user's preferred playlists, artists,albums, tracks, and the like by aggregating data from the two or morestreaming audio services, as compared with a streaming audio servicethat only has access to data generated through use of its own service.

Moreover, in some implementations, in addition to the data shared fromthe streaming audio service servers 906 b, the media playback systemcontrol servers 906 a may collect usage data from the MPS 100 over thelinks 903 a, after receiving user permission. This may include dataindicating a user's saved or preferred media items on a zone basis.Different types of music may be preferred in different rooms. Forinstance, a user may prefer upbeat music in the Kitchen 101 h and moremellow music to assist with focus in the Office 101 e.

Using the data indicating a user's saved or preferred playlists,artists, albums, tracks, and the like, the media playback system controlservers 906 a may identify names of playlists, artists, albums, tracks,and the like that the user is likely to refer to when providing playbackcommands to the NMDs 703 via voice input. Data representing these namescan then be transmitted via the links 903 a and the network 904 to theNMDs 703 and then added to the library of the local NLU 779 as keywords.For instance, the media playback system control servers 906 a may sendinstructions to the NMDs 703 to include certain names as keywords in thelibrary of the local NLU 779. Alternatively, the NMDs 703 (or anotherdevice of the MPS 100) may identify names of playlists, artists, albums,tracks, and the like that the user is likely to refer to when providingplayback commands to the NMDs 703 via voice input and then include thesenames in the library of the local NLU 779.

Due to such customization, similar voice inputs may result in differentoperations being performed when the voice input is processed by thelocal NLU 779 as compared with processing by a VAS. For instance, afirst voice input of “Alexa, play me my favorites in the Office” maytrigger a VAS wake word event, as it includes a VAS wake word (“Alexa”).A second voice input of “Play me my favorites in the Office” may triggera command keyword, as it includes a command keyword (“play”).Accordingly, the first voice input is sent by the NMD 703 to the VAS,while the second voice input is processed by the local NLU 779.

While these voice inputs are nearly identical, they may cause differentoperations. In particular, the VAS may, to the best of its ability,determine a first playlist of audio tracks to add to a queue of theplayback device 102 f in the office 101 e. Similarly, the local NLU 779may recognize keywords “favorites” and “kitchen” in the second voiceinput. Accordingly, the NMD 703 performs the voice command of “play”with parameters of <favorites playlist> and <kitchen 101 h zone>, whichcauses a second playlist of audio tracks to be added to the queue of theplayback device 102 f in the office 101 e. However, the second playlistof audio tracks may include a more complete and/or more accuratecollection of the user's favorite audio tracks, as the second playlistof audio tracks may draw on data indicating a user's saved or preferredplaylists, artists, albums, and tracks from multiple streaming audioservices, and/or the usage data collected by the media playback systemcontrol servers 906 a. In contrast, the VAS may draw on its relativelylimited conception of the user's saved or preferred playlists, artists,albums, and tracks when determining the first playlist.

To illustrate, FIG. 11 shows a table 1100 illustrating the respectivecontents of a first and second playlist determined based on similarvoice inputs, but processed differently. In particular, the firstplaylist is determined by a VAS while the second playlist is determinedby the NMD 703 (perhaps in conjunction with the media playback systemcontrol servers 906 a). As shown, while both playlists purport toinclude a user's favorites, the two playlists include audio content fromdissimilar artists and genres. In particular, the second playlist isconfigured according to usage of the playback device 102 f in the Office101 e and also the user's interactions with multiple streaming audioservices, while the first playlist is based on the multiple user'sinteractions with the VAS. As a result, the second playlist is moreattuned to the types of music that the user prefers to listen to in theoffice 101 e (e.g., indie rock and folk) while the first playlist ismore representative of the interactions with the VAS as a whole.

A household may include multiple users. Two or more users may configuretheir own respective user profiles with the MPS 100. Each user profilemay have its own user accounts of one or more streaming audio servicesassociated with the respective user profile. Further, the media playbacksystem control servers 906 a may maintain or have access to dataindicating each user's saved or preferred playlists, artists, albums,tracks, genres, and the like, which may be associated with the userprofile of that user.

In various examples, names corresponding to user profiles may bepopulated in the library of the local NLU 779. This may facilitatereferring to a particular user's saved or preferred playlists, artists,albums, tracks, or genres. For instance, when a voice input of “PlayAnne's favorites on the patio” is processed by the local NLU 779, thelocal NLU 779 may determine that “Anne” matches a stored keywordcorresponding to a particular user. Then, when performing the playbackcommand corresponding to that voice input, the NMD 703 adds a playlistof that particular user's favorite audio tracks to the queue of theplayback device 102 c in the patio 10 i. In some embodiments, differentNMDs 703 of the MPS 100 have local NLUs 779 storing keywords associatedwith different user profiles. For example, a first NMD can have a firstNLU 779 with keywords associated with a first user, Anne. Meanwhile, asecond NMD can have a second NLU 779 storing keywords associated with asecond user, Bryan.

In some cases, a voice input might not include a keyword correspondingto a particular user, but multiple user profiles are configured with theMPS 100. In some cases, the NMD 703 may determine the user profile touse in performing a command using voice recognition. Alternatively, theNMD 703 may default to a certain user profile. Further, the NMD 703 mayuse preferences from the multiple user profiles when performing acommand corresponding to a voice input that did not identify aparticular user profile. For instance, the NMD 703 may determine afavorites playlist including preferred or saved audio tracks from eachuser profile registered with the MPS 100.

The TOT cloud servers 906 c may be configured to provide supportingcloud services to the smart devices 990. The smart devices 990 mayinclude various “smart” internet-connected devices, such as lights,thermostats, cameras, security systems, appliances, and the like. Forinstance, an TOT cloud server 906 c may provide a cloud servicesupporting a smart thermostat, which allows a user to control the smartthermostat over the internet via a smartphone app or website.

Accordingly, within examples, the TOT cloud servers 906 c may maintainor have access to data associated with a user's smart devices 990, suchas device names, settings, and configuration. Under appropriateconditions (e.g., after receiving user permission), the TOT cloudservers 906 c may share this data with the media playback system controlservers 906 a and/or the NMD 703 via the links 903 c. For instance, theTOT cloud servers 906 c that provide the smart thermostat cloud servicemay provide data representing such keywords to the NMD 703, whichfacilitates populating the library of the local NLU 779 with keywordscorresponding to the temperature.

Yet further, in some cases, the TOT cloud servers 906 c may also providekeywords specific to control of their corresponding smart devices 990.For instance, the TOT cloud server 906 c that provides the cloud servicesupporting the smart thermostat may provide a set of keywordscorresponding to voice control of a thermostat, such as “temperature,”“warmer,” or “cooler,” among other examples. Data representing suchkeywords may be sent to the NMDs 703 over the links 903 and the network904 from the TOT cloud servers 906 c.

As noted above, some households may include more than NMD 703. Inexample implementations, two or more NMDs 703 may synchronize orotherwise update the libraries of their respective local NLU 779. Forinstance, a first NMD 703 and a second NMD 703 may share datarepresenting the libraries of their respective local NLU 779, possiblyusing a network (e.g., the network 904). Such sharing may facilitate theNMDs 703 being able to respond to voice input similarly, among otherpossible benefits. As noted elsewhere herein, in various embodiments thelibraries of the respective local NLUs 779 of the NMD 703 can beidentical or may vary from one to the next. In operation, voice inputreceived at one NMD may be processed for keyword detection using localNLUs 779 of multiple different NMDs. This can advantageously expand thenumber of possible keywords to be identified in the voice input, asdifferent NMDs can have NLUs 779 that support different libraries ofkeywords. For example, if a voice input contains a keyword that is notstored on the library of a first NLU 779 of a first NMD 703, the keywordmay nonetheless be present in a library of a second NLU 779 of a secondNMD 703. In some embodiments, this can also allow cross-checking ofkeyword detection to improve confidence and lower error rates.

In some instances, an NMD 703 that receives a voice input canselectively transmit the voice input to some but not all of the otherNMDs 703 on the local network to perform keyword detection. For example,a first NMD 703 may identify the keyword “Spotify” in a voice input.Based on this keyword detection, the first NMD may transmit the voiceinput to a second NMD that is identified as having a library associatedwith Spotify commands (or media streaming service commands moregenerally). Similarly, if the first NMD 703 identifies the keyword“thermostat” in a voice input, the first NMD may transmit the voiceinput to a third NMD on the local network that is identified as having alibrary associated with IOT commands. Additionally or alternatively, afirst NMD 703 may process voice input via its ASR and then, based on oneor more keywords identified via the ASR, pass the ASR output to a secondNMD for processing via its own NLU, which may include a differentlibrary of keywords associated with different intent categories. As oneexample, a first NMD 703 may identify the keyword “Spotify” in voiceinput via its onboard ASR. Based on this identified keyword, the outputof the ASR (e.g., a text string representing the voice input) can betransmitted to a particular NMD having an NLU with a library of keywordsassociated with Spotify-specific commands. As a result, even if theidentified keyword (in this example, “Spotify”) is not sufficient toidentify an associated intent, the identified keyword via the ASR issufficient to direct the ASR output to an appropriate NLU for intentevaluation. In such a configuration, an environment may include multipledevices each having one or more ASRs and each having different NLUs withintent engines configured to identify intents based on the ASR output.For example, one device may have a local NLU configured to determineintents relating to music playback, while another device has an NLUconfigured to determine intents relating to home automation. In anotherexample, one device could have an NLU with a rules-based intent engine,while a second device may have an NLU with a statistical intent engine,and a third device has a hybrid intent engine. Accordingly, an ASRoutput can be routed from one device to one or more different NLUshaving different libraries and configured to identify differentcategories of intents.

In some embodiments, the ASR output can be evaluated in context todetermine which device should receive the ASR output for intentprocessing. For example, the ASR output may have an associatedconfidence score associated with different text strings. In someinstances, even if a particular text string has a low associatedconfidence, the context (i.e., the other words or phrases in the ASRoutput) may raise the overall confidence. For example, based on a userspeaking the word “Spotify” in noisy conditions, the ASR output mayprovide a 40% confidence that the term “Spotify” is detected, and a 50%confidence that the term “notify” is detected. However, if the same ASRoutput also contains higher confidence in the terms “play” and “myfavorites,” then the ASR output may be modified to assign a higherconfidence to the term “Spotify,” since, in the context of “play myfavorites,” the overall likelihood of “Spotify” in the voice input ishigher than “notify.” In response, the ASR output may be transmitted toan NMD having a local NLU with a library of keywords associated withSpotify commands.

In some instances, the system can receive feedback regarding whether theanalysis was correct (i.e., whether the user is satisfied with theidentified intent). Over time, the distribution of NLUs may be organizedsuch that the intent engines evolve over time towards higherperformance. For example, over time, each NMD may apply small changes toits intent engine (e.g., changing supported keywords, changingstatistical thresholds for identification of intent, changing internalrules for intent determination, etc.). Based on collected feedback,whichever device proves to be correct most often may then be copied intoother devices. These devices may then again make small changes to theirrespective intent engines and the cycle repeats.

In some embodiments, the various NLUs distributed among a plurality ofdevices in the user environment can be configured such that each NLUperforms a specific function or set of functions on ASR output (whetherreceived from that particular NMD or from another local NMD). Forexample, one NLU may perform parsing, another may tag keywords, anothermay perform grammar analysis, etc.

In some embodiments, one or more of the components described above canoperate in conjunction with the microphones 720 to detect and store auser's voice profile, which may be associated with a user account of theMPS 100. In some embodiments, voice profiles may be stored as and/orcompared to variables stored in a set of command information or datatable. The voice profile may include aspects of the tone or frequency ofa user's voice and/or other unique aspects of the user, such as thosedescribed in previously referenced U.S. patent application Ser. No.15/438,749.

In some embodiments, one or more of the components described above canoperate in conjunction with the microphones 720 to determine thelocation of a user in the home environment and/or relative to a locationof one or more of the NMDs 103. Techniques for determining the locationor proximity of a user may include one or more techniques disclosed inpreviously referenced U.S. patent application Ser. No. 15/438,749, U.S.Pat. No. 9,084,058 filed Dec. 29, 2011, and titled “Sound FieldCalibration Using Listener Localization,” and U.S. Pat. No. 8,965,033filed Aug. 31, 2012, and titled “Acoustic Optimization.” Each of theseapplications is herein incorporated by reference in its entirety.

V. Example Locally Distributed Keyword Detection

As noted above, in media playback systems 100 having multiple NMDs 703,keyword detection can be improved by leveraging the presence of multipleNMDs 703 in a number of ways. In some embodiments, detection of keywordscan be locally distributed among one or more NMDs 703 connected over anetwork (e.g., a local area network). For example, a first NMD 703 mayreceive a voice input and generate input sound data to be analyzed fordetection of a command keyword as described previously. Concurrently orsequentially, the input sound data may be transmitted from the first NMDto a second NMD for evaluation and potential keyword detection.

In some embodiments, the first NMD can transmit input sound data (e.g.,signal S_(DS) as output from the VCC 760 of FIG. 7A) to the second NMD,which can then be evaluated via a command-keyword engine 771 of thesecond NMD, including evaluation using a local NLU 779 of the second NMD703. In some embodiments, the first NMD can transmit the ASR output(e.g., signal S_(ASR) of FIG. 7A), which can be evaluated by a local NLU779 of the second NMD without first being evaluated for command-keyworddetection.

The results of the keyword-detection processes performed by each of theNMDs 703 (e.g., the output of the respective command-keyword engine 771of each NMD 703) can be compared to cross-check or confirm keyworddetection. Such cross-checking can decrease error rates in keyworddetection, for example by reducing the rate of false positives.Additionally or alternatively, different NMDs 703 can have differentNLUs 779 with different libraries of keywords, and accordingly multipleNMDs 703 can be used to expand the total library of supported keywordsin a user's environment. Accordingly, using multiple NMDs 703 toevaluate input sound data can improve local keyword detection bydecreasing error rates and/or by expanding the number of supportedkeywords, thereby allowing keyword detection even in cases where asingle NMD 703 may be unable to verify the presence of a keyword in theinput sound data.

In some embodiments, processing the voice input via the NLU 779 isperformed in response to detection of a command keyword viacommand-keyword engine 771 a. Additionally or alternatively, voice inputcan be processed via the NLU 779 in response to detection of a wake-wordevent (e.g., detection of a VAS wake-word via the VAS wake-word engine770 a) or any other suitable trigger event. In such embodiments,following detection of a VAS wake word in voice input, the NLUs 779 ofmultiple NMDs can cooperate to provide an expanded library of keywordsand/or to cross-check keyword detection results as described elsewhereherein.

FIG. 11 is a flow diagram showing an example method 1100 for locallydistributed keyword detection. The keyword may be detected by leveragingthe operation of two or more NMDs together. The method 1100 may beperformed by a networked microphone device, such as the NMD 120 (FIG.1A), which may include features of the NMD 703 (FIG. 7). In someimplementations, the NMD is implemented within a playback device, asillustrated by the playback device 102 r (FIG. 1G).

At block 1102, the method 1100 involves receiving input sound datarepresenting sound detected by one or more microphones of an NMD 703(which may be part of a playback device). For instance, the NMD 703 maydetect sound via the microphones 720 (FIG. 7A). Further, the NMD 703 mayprocess the detected sound using one or more components of the VCC 760to produce input sound data for further processing.

At block 1104, the method 1100 involves detecting, via a command-keywordengine (e.g., command-keyword engine 771 of FIG. 7A), a first commandkeyword in a first voice input represented in the input sound data. Todetermine whether the voice input includes a command keyword, thecommand-keyword engine 771 a may analyze the sound-data stream S_(DS)(FIG. 7A). In particular, the ASR 772 may transcribe the sound-datastream S_(DS) to text (e.g., the signal S_(ASR)) and the local NLU 779may determine that words matching a keyword are in the transcribed text.In other examples, the command-keyword engine 771 a may use one or morekeyword identification algorithms on the sound-data stream S_(DS). Otherexamples are possible as well.

At block 1106, the method 1100 includes determining, via a first NLU,whether the input sound data includes a keyword within a firstpredetermined library of keywords. For example, the local NLU 779 maydetect that the input sound data at least one keyword (or any keywords)from the library of the local NLU 779. The local NLU 779 is configuredto analyze the signal S_(ASR) to spot (i.e., detect or identify)keywords in the voice input. The local NLU can also determine an intentbased on the at least one keyword. For instance, the local NLU 779 maydetermine an intent from one or more keyword in the input sound data. Asindicated above, the keywords in the library of the local NLU 779 cancorrespond to parameters. The keyword(s) in a voice input may indicatean intent, such as to play particular audio content in a particularzone.

At block 1108, the method 1200 involves transmitting, via a local areanetwork, the input sound data to a second device. The second device canbe, for example, a second NMD 703 having a second command-keyword engine771 and a second NLU with a second predetermined library of keywords. Insome embodiments, the second predetermined library of keywords of thesecond NMD can be substantially or completely identical to the firstpredetermined library of the first NMD. In some embodiments, some or allof the keywords present in the first predetermined library can vary fromthose present in the second predetermined library. The use of two (ormore) different predetermined libraries introduces the possibility ofdramatically increasing the total number of supported keywords. As oneexample, if each NMD has a library with approximately 10,000 keywords,then two NMDs having completely non-overlapping libraries may provide acombined 20,000 keywords for the media playback system of which the twoNMDs are a part. In operation, voice input received at any one of theNMDs within the system can be processed for keyword detection amongmultiple NMDs. As such, a single voice input can be evaluated fordetection of keywords supported by two or more of the NMDs, therebysignificantly increasing the total library of keywords supported by thesystem.

In some embodiments, the different libraries can include dedicateddirectories. For example, the first predetermined library can includekeywords that are associated with a first intent category (e.g.,transport commands), while the predetermined library can includekeywords that are associated with a second intent category (e.g.,Internet-of-Things (IOT) commands or media service provider commands).By supporting different directories, a voice input received via thefirst NMD can be processed for detection of keywords associated withdifferent intent categories, even if a single library on the first NMDwould be unable to store or support the keywords associated with each ofthe different intent categories.

In some embodiments, the different libraries supported by the differentNMDs can include partitions. For example, the first predeterminedlibrary can include a first partition of shared keywords and a secondpartition of dedicated keywords. The second predetermined library maythen include a first partition of the shared keywords that issubstantially or completely identical to the first partition of firstpredetermined library. The second predetermined library can also includea second partition of dedicated keywords that is substantially orcompletely distinct from the second partition of the first predeterminedlibrary. For example, the dedicated partition of the first predeterminedlibrary can store keywords associated with IOT commands, while thededicated partition of the second predetermined library can storekeywords associated with streaming media services commands. In someembodiments, the shared keywords can include keywords used most often(e.g., common transport commands such as “pause,” “play,” etc.). Bystoring the most commonly used commands in libraries of each NMD, thesystem may more consistently and responsively detect these keywords andperform associated operations. In some embodiments, there may bemultiple partitions supported by each NMD, none of which is completelyshared with other libraries.

At block 1110, a response from the second playback device is received atthe first playback device. The response can include results of thesecond playback device evaluating the input sound data to identifykeywords and/or an intent. In some embodiments, the response can includeboth any identified keyword(s) as well as associated confidence scoresor other indicia relating to the likelihood of a matched keyword. If thelibraries of the respective NLUs 779 of the respective first and seconddevices are different, it may be the case that the first NLU does notidentify a keyword in the input sound data, while the second NLU of thesecond device does identify a keyword in the input sound data. Althoughthese examples are described with respect to two NMDs, this process canbe extended to any number of different NMDs, any or all of which canhave different NLUs storing different libraries of keywords.

Finally, at block 1112, the device performs an action based on an intentdetermined by at least one of the first NLU or the second NLU. In oneexample, the first NLU of the first device does not identify a keywordmatch, while the response from the second NLU indicates an identifiedkeyword (and, optionally, a sufficiently high confidence score). As aresult, the first device may perform a command corresponding to thekeyword identified via the second NLU. For instance, the NMD 703 mayperform a playback command, which may involve generating one or moreinstructions to perform the command, which cause the target playbackdevice(s) to perform the first playback command.

In some embodiments, instructing the target playback device(s) toperform the first playback command may be explicitly or implicitlydefined. For example, the target playback devices may be explicitlydefined by reference in the voice input 780 to the name(s) of one ormore playback devices (e.g., by reference to a zone or zone group name).Alternatively, the voice input might not include any reference to thename(s) of one or more playback devices and instead may implicitly referto playback device(s) 102 associated with the NMD 703. Playback devices102 associated with the NMD 703 may include a playback deviceimplementing the NMD 703, as illustrated by the playback device 102 dimplementing the NMD 103 d (FIG. 1B)) or playback devices configured tobe associated (e.g., where the playback devices 102 are in the same roomor area as the NMD 703).

Within examples, performing an action may involve transmitting one ormore instructions over one or more networks. For instance, the NMD 703may transmit instructions locally over the network 903 to one or moreplayback devices 102 to perform instructions such as transport commands(FIG. 10), similar to the message exchange illustrated in FIG. 6.Further, the NMD 703 may transmit requests to the streaming audioservice service(s) 906 b to stream one or more audio tracks to thetarget playback device(s) 102 for playback over the links 903 (FIG. 10).Alternatively, the instructions may be provided internally (e.g., over alocal bus or other interconnection system) to one or more software orhardware components (e.g., the electronics 112 of the playback device102).

FIG. 12 is a flow diagram showing another example method 1200 forlocally distributed keyword detection. The method 1200 can facilitatecross-checking of keyword detection either among multiple NMDs or withindifferent subsets of input sound data captured by microphones of asingle NMD. As with the method 1100, the method 1200 may be performed bya networked microphone device, such as the NMD 103 s (FIG. 1A), whichmay include features of the NMD 703 (FIG. 7A). In some implementations,the NMD is implemented within a playback device, as illustrated by theplayback device 102 r (FIG. 1G).

At block 1202, the method 1200 involves receiving input sound datarepresenting sound detected by one or more microphones of an NMD. Atblock 1204, the method 1200 involves detecting, via a command-keywordengine (e.g., command-keyword engine 771 of FIG. 7A), a first commandkeyword in a first voice input represented in the input sound data. Atblock 1206, the method 1200 includes determining, via a first NLU,whether the input sound data includes a keyword within a firstpredetermined library of keywords. Blocks 1202, 1204, and 1206 can becarried out similar to blocks 1102, 1104, and 1106 described above withrespect to the method 1100 of FIG. 11.

With continued reference to FIG. 12, at block 1208, the method 1200involves receiving, at the first playback device, an indication that asecond NLU has made a second determination that the input sound dataincludes at least one keyword within the predetermined library ofkeywords. In some embodiments, the second NLU can store a library ofkeywords that substantially or identically corresponds to thepredetermined library of keywords stored by the first NLU. In otherembodiments, the second NLU stores a library of keywords that partiallybut not completely overlaps with the library of keywords stored by thefirst NLU. In the case of overlapping or shared keywords that arepresent in libraries of both the first NLU and the second NLU, thesecond NLU can cross-check or confirm detection of such shared keywordsby the first NLU. The response can include results of the second NLUevaluating the input sound data to identify keywords and/or an intent.In some embodiments, the response includes both any identifiedkeyword(s) as well as associated confidence scores or other indiciarelating to the likelihood of a matched keyword.

In some embodiments, the second NLU can be part of a second NMD having asecond keyword engine. For example, the second NMD may separately detectthe same user speech as voice input and process the voice input via thesecond NLU to determine whether a keyword is present. The results ofthis determination can then be transmitted over a local area network tothe first device. In other embodiments, the first device may transmit,via a local area network, the input sound data to the second device forprocessing via its second NLU. The second device may then provide aresponse to the first device that includes a determination regardingwhether a keyword was identified via the second NLU.

In some embodiments, the second NLU is not on a different device, but ison the same device and configured to evaluate different input sound datafrom the first NLU. For example, the NMD may have multiple microphonesconfigured to generate sound data from a voice input. A first subset ofthe microphones may be used to generate first input sound data that canbe evaluated to identify a keyword via the first NLU. A second subset ofthe microphones may be used to generate second input sound data from thesame voice input that can be evaluated via the second NLU to identify akeyword. For example, the NMD 703 can be configured to generate a firstsound-data stream S_(DS) representing data obtained from a first subsetof the microphones 720 (FIG. 7A), and to generate a second sound-datastream S_(DS) representing data obtained from a second subset of themicrophones 720 that is different from the first. Optionally, in someembodiments the subsets of the microphones can include some overlapping.Additionally, in some embodiments there may be three, four, five, ormore different sound-data streams S_(DS) generated using differentsubsets of microphones or other variations in processing of voice input.These different sound-data streams S_(DS) can be separately evaluatedfor keyword detection. As a result, a single NMD may generate twodeterminations as outputs of keyword-detection engines: a firstdetermination involving the first NLU analyzing the first input sounddata, and a second determination involving the second NLU analyzing thesecond input sound data. In some embodiments the same NLU can be used toprocess each of the two (or more) different sound-data streams S_(DS)for comparison.

At block 1210, the method involves comparing the first and seconddeterminations and, based at least in part on the comparison, foregoingfurther processing. If, for example, the results do not match (e.g., thefirst NLU identifies the word “pause” but the second NLU does notidentify any keyword), the NMD may decline to forego further processingof the input sound data. This reflects the assessment that detection ofthe word “pause” via the first NLU is likely a false positive, due tothe lack of confirmation from the second NLU. If, in contrast, thedeterminations did match, the NMD may perform an action corresponding tothe identified keyword. In this way, a second NLU is leveraged tocross-check the determination of the first NLU.

FIGS. 13-15 illustrate examples scenarios in which one or more NMDshaving local NLUs communicate and perform actions in accordance withaspects of the disclosure. The environment includes a first NMD 103 dhaving a first NLU (“NLU1”), a second NMD 103 i having a second NLU(“NLU2”), and a third NMD 103 e having a third NLU (“NLU3”). Each of theNMDs are in communication with one another over a local area networkfacilitated by the router 110. The NMDs may also be in communicationwith one or more remote computing devices 106 over a wide area networkvia the router 110. Each of the NMDs may include features of the NMD 703(FIG. 7A). In some implementations, the NMDs may be implemented within aplayback device, as illustrated by the playback device 102 r (FIG. 1G).Although these examples are shown with three NMDs, these processes canbe applied to fewer (e.g., two) or greater (e.g., three, four, or more)numbers of NMDs within the environment.

As described in more detail below, in various embodiments each of NLU1,NLU2, and NLU3 may store predetermined libraries of keywords that aresubstantially or completely identical, partially overlapping, orcompletely non-overlapping. In example implementations, the individualNMDs 103 d, 103 i, and 103 e may synchronize or otherwise update thelibraries of their respective local NLUs. For instance, the NMDs 103 d,103 i, and 103 e may share data representing the libraries of theirrespective local NLUs NLU1, NLU2, and NLU3, possibly using a network.

FIGS. 13 and 14 illustrate examples in which multiple NMDs are leveragedto provide an increased number of keywords supported by the combinedNLUs within the environment. As noted previously, any one NLU maysupport a relatively limited number of keywords (e.g., having a libraryof approximately 10,000 predetermined keywords). Accordingly, it can beadvantageous to store different keywords or combinations of keywords inthe libraries of different NLUs associated with different NMDs withinthe environment.

With respect to FIG. 13, the NLU1 may store a first predeterminedlibrary of keywords, NLU2 stores a second predetermined library ofkeywords, and NLU3 stores a third predetermined library of keywords. Inthis example, each of the libraries of keywords can be substantially orcompletely non-overlapping. As a result, if each library supportsapproximately 10,000 keywords, then the combined libraries supportapproximately 30,000 keywords, thereby dramatically increasing thenumber of keywords available for local keyword detection.

As an example, the user speaks a command to the first NMD 103 d to “PlayHey Jude by the Beatles”. The first NMD 103 d detects the user speech asvoice input which is processed using a command-keyword engine asdescribed previously herein. This processing includes searching apredetermined library of keywords stored by NLU1. In this example, NLU1finds a match for the “play” command but does not find a match for “HeyJude.” In parallel with this processing via NLU1 (or subsequent to thedetermination of no match via NLU1), the first NMD 103 d transmits arequest to the second NMD 103 i and third NMD 103 e to perform keyworddetection on the voice input via NLU2 and NLU3. Each of these NMDs mayprocess the voice input from the first NMD 103 d to detect a match withkeywords stored in their respective libraries. If, for example, thesecond NMD 103 i detects a match with “Hey Jude,” the second NMD 103 ican provide a response to the first NMD 103 d that include instructionsto stream the song “Hey Jude” from Apple Music or other cloud-basedmusic service. Notably, this request for streaming content from acloud-based provider can be performed without requiring the interventionof a VAS. If, in contrast, neither the second NMD 103 i nor the thirdNMD 103 e identifies a matching keyword, then the first NMD 103 d mayeither (a) provide a response to the user that the command cannot beprocessed (e.g., a voice output stating “I'm sorry, I couldn'tunderstand that request”) and/or (b) transmits the voice input to a VAS(e.g., VAS 190 of FIG. 1B) for remote processing.

In this example, it can be seen that locally distributing keywords amongdifferent libraries stored by different NMDs can increase the totalnumber of supported keywords for local processing without recourse to aremote VAS. Local processing may provide an improved user experience, asit eliminates the latency associated with transmission of requests to aremote VAS for processing.

FIG. 14 illustrates another example environment in which keywords aredistributed among the three NMDs having respective NLUs. In thisexample, however, each NLU has two associated partitions. Asillustrated, each of the NLUs includes a shared partition w, while NLU1also includes a dedicated partition x, NLU2 includes a dedicatedpartition y, and NLU3 includes a dedicated partition z. Although thisexample illustrates each NLU having the same shared partition and onededicated partition, in various embodiments any number of partitions maybe shared only among some of the NLUs within the environment, andadditionally any number of dedicated partitions may be stored by one ormore of the NLUs. In some embodiments, the shared partition x caninclude keywords associated with the most frequently used commands,while the dedicated partition x, y, and z can each store keywordsassociated with less frequently commands. Such a configuration mayreduce access time or latency by requiring searching across the networkto other NLUs only when the local NLU of the NMD that receives the voiceinput is not found to contain the keyword. In the cases of most commonlyused phrases (e.g., “pause” or other transport commands), each NLU isequipped with corresponding keywords and accordingly the NMD can respondto the user's voice input without requiring the cooperation of otherNMDs on the network.

In some embodiments, the dedicated partitions associated with differentNLUs can correspond to different intent categories. For example,partition x can store keywords associated with IOT commands, partition ycan store keywords associated with media service provider commands, andpartition z can store keywords associated with user alarms and timers.In some embodiments, voice input received at one NMD can be selectivelyrouted to another NMD for processing via its NLU based on the associateddedicated partition of that NLU. For example, if the first NMD 103 didentifies the keyword “doorbell” in a voice input, the first NMD maytransmit the voice input to the third NMD 103 e, whose dedicatedpartition z contains keyword associated with IOT commands.

FIGS. 13 and 15 illustrate examples in which multiple NMDs can beleveraged to cross-check or confirm keyword determinations made byindividual NMDs. For example, two or more NMDs may detect at least onekeyword in voice input. By comparing determinations among the NMDs, theassociated confidence of keyword detection can be increased, and theerror rate thereby reduced. In these examples, the NLUs of theindividual NMDs may have at least partially overlapping libraries ofkeywords, or in some examples can have completely identical libraries ofkeywords.

With reference back to FIG. 13, a user's voice input can be separatelyprocessed by two or more NMDs for keyword detection and the results canbe compared or otherwise combined to make a final determination. Forexample, the user may provide a voice input detected by both the firstNMD 103 d and the second NMD 103 i. Each of these NMDs may process thevoice input (e.g., using their respective NLUs NLU1 and NLU2) toidentify one or more keywords in the voice input. If the results match(either exactly or generally), then one of the NMDs may proceed toprocess the command. If the results of the two determinations do notmatch, then the NMDs may disregard the command or perform some otherintervention, such as prompting the user to restate her request. Forexample, if the first NMD 103 d detects that the user spoke “play songsby train” and the second NMD 103 i detects that the user spoke “playblame it on the rain,” the system may disregard the command or performsome other intervention. As noted above, in some embodiments therespective NLUs can include only partially overlapping libraries (e.g.,each having a shared partition w, while having other non-shared,dedicated partitions as in FIG. 14). In such embodiments, the system canbe configured to perform such cross-checking only on keywords that arefound in the overlapping or shared keywords of the libraries.

With reference to FIG. 15, in some instances cross-checking can beperformed not only between individual NMDs, but between differentsubsets of the input sound data as detected by an individual NMD. Asillustrated, the first NMD 103 d includes a first NLU1 and four lanesLane 1 a-1 d. Similarly, the second NMD 103 i includes the second NLU2and four lanes 2 a-2 d, and the third NMD 103 e includes the second NLU3and four lanes 3 a-3 d. As used herein, a “lane” can refer to inputsound data generated from a single microphone or from any combination ofmicrophones of the NMD. For example, one or more individual microphonesof the first NMD 103 d can be used to generate input sound datacorresponding to a first lane la, while a different subset ofmicrophones is used to generate input sound data corresponding to asecond lane lb, etc. Note that in some instances these subsets can atleast partially overlap, such that sound data captured by a singlemicrophone may be used to generate data for more than one lane. Inoperation, the input sound data can differ from one lane to the next,and accordingly the NLU1 may return different results (e.g., identifydifferent keywords, or fail to identify any keyword at all) whenanalyzing the input sound data of the different lanes. These differentinstances of input sound data can allow a single NMD to cross-check anykeyword determination by confirming that the NLU identifies the samekeyword across some or all of the lanes.

In some embodiments, a single NMD may include multiple different NLUs,each of which is configured to analyze the output of some but not all ofthe lanes. For example, the first NMD 103 d could have four NLUs, eachof which is configured to analyze the input sound data of one of thelanes 1 a-1 d. These NLUs could have only partially overlappinglibraries of keywords, such that together the total number of storedkeywords is expanded, while still permitting cross-checking fordetermination of keywords that are shared across two or more NLUs. Insome embodiments, such cross-checking can be performed across NMDs. Forexample, a detection of a keyword using any one lanes 1 a-d of the firstNMD 103 d can be compared with detection of a keyword using any one oflanes 2 a-2 d of the second NMD 103 i. The lanes and NMDs can becombined in any number of ways to detect keywords and to compare resultsto increase confidence in keyword detection.

Accordingly, there are numerous advantages to distributing keyworddetection among multiple different devices over a local network. Thevarious aspects of locally distributed keyword detection described inthe different examples above can be combined, modified, re-ordered, orotherwise altered to achieve the desired implementation.

Conclusion

The description above discloses, among other things, various examplesystems, methods, apparatus, and articles of manufacture including,among other components, firmware and/or software executed on hardware.It is understood that such examples are merely illustrative and shouldnot be considered as limiting. For example, it is contemplated that anyor all of the firmware, hardware, and/or software aspects or componentscan be embodied exclusively in hardware, exclusively in software,exclusively in firmware, or in any combination of hardware, software,and/or firmware. Accordingly, the examples provided are not the onlyway(s) to implement such systems, methods, apparatus, and/or articles ofmanufacture.

The specification is presented largely in terms of illustrativeenvironments, systems, procedures, steps, logic blocks, processing, andother symbolic representations that directly or indirectly resemble theoperations of data processing devices coupled to networks. These processdescriptions and representations are typically used by those skilled inthe art to most effectively convey the substance of their work to othersskilled in the art. Numerous specific details are set forth to provide athorough understanding of the present disclosure. However, it isunderstood to those skilled in the art that certain embodiments of thepresent disclosure can be practiced without certain, specific details.In other instances, well known methods, procedures, components, andcircuitry have not been described in detail to avoid unnecessarilyobscuring aspects of the embodiments. Accordingly, the scope of thepresent disclosure is defined by the appended claims rather than theforgoing description of embodiments.

When any of the appended claims are read to cover a purely softwareand/or firmware implementation, at least one of the elements in at leastone example is hereby expressly defined to include a tangible,non-transitory medium such as a memory, DVD, CD, Blu-ray, and so on,storing the software and/or firmware.

The present technology is illustrated, for example, according to variousaspects described below. Various examples of aspects of the presenttechnology are described as numbered examples (1, 2, 3, etc.) forconvenience. These are provided as examples and do not limit the presenttechnology. It is noted that any of the dependent examples may becombined in any combination, and placed into a respective independentexample. The other examples can be presented in a similar manner.

Example 1: A playback device of a media playback system, the playbackdevice comprising: at least one speaker; one or more microphonesconfigured to detect sound; a network interface; one or more processors;and data storage having instructions stored thereon that are executableby the one or more processors to cause the playback device to performfunctions comprising: receiving input sound data representing the sounddetected by the one or more microphones; detecting, via acommand-keyword engine, a first command keyword in a first voice inputrepresented in the input sound data, wherein the command-keyword engineis configured to (a) process input sound data representing the sounddetected by the at least one microphone and (b) generate acommand-keyword event when the command-keyword engine detects, in theinput sound data, at least one of a plurality of keywords supported bythe command-keyword engine; in response to detecting the first commandkeyword, making a first determination, via a first local naturallanguage unit (NLU), whether the input sound data includes at least onekeyword within a first a first predetermined library of keywords fromwhich the first NLU is configured to determine an intent of a givenvoice input; receiving an indication of a second determination, made bya second NLU, whether the input sound data includes at least one keywordfrom a second predetermined library of keywords; comparing the resultsof the first determination with the second determination; and based onthe comparison, foregoing further processing of the input sound data.

Example 2: The playback device of claim 1, wherein the functions furthercomprise: detecting, via the command-keyword engine, a second commandkeyword in a second voice input represented in second input sound data;in response to detecting the second command keyword, making a thirddetermination, via the first local NLU, that the second input sound dataincludes one or more keywords from the first predetermined library ofkeywords; receiving an indication of a fourth determination made by thesecond NLU that the second input sound data includes one or morekeywords from the second predetermined library of keywords; comparingthe results of the third determination with the fourth determination;and based on the comparison, performing a command according to one ormore parameters corresponding to the at least one keyword in the secondinput sound data.

Example 3: The playback device of Example 2, wherein comparing theresults of the third determination with the fourth determinationcomprises confirming one or more keywords of the third determination areidentical to the one or more keywords of the fourth determination.

Example 4: The playback device of any one of the preceding Examples,wherein receiving an indication of a second determination made by thesecond NLU comprises receiving, over a local area network via thenetwork interface, the indication from a second playback device havingthe second NLU.

Example 5: The playback device of any one of the preceding Examples,wherein: the playback device comprises a plurality of microphones; thefirst NLU is configured to detect, in input sound data detected by afirst subset of the microphones, keywords from the first predeterminedlibrary of keywords; and the second NLU is configured to detect, ininput sound data detected by a second subset of the microphones,keywords from the second predetermined library of keywords.

Example 6: The playback device of any one of the preceding Examples,wherein the first predetermined library of keywords includes one or morekeywords that are not included in the second predetermined library ofkeywords.

Example 7: The playback device of any one of the preceding Examples,further comprising a voice assistant service (VAS) wake-word engineconfigured to receive input sound data representing the sound detectedby the at least one microphone and generate a VAS wake-word event whenthe VAS wake-word engine detects a VAS wake word in the input sounddata, wherein the playback device streams sound data representing thesound detected by the at least one microphone to one or more servers ofthe VAS when the VAS wake-word event is generated.

Example 8: A method comprising: receiving input sound data representingthe sound detected by one or more microphones of a playback device;detecting, via a command-keyword engine, a first command keyword in afirst voice input represented in the input sound data, wherein thecommand-keyword engine is configured to (a) process input sound datarepresenting the sound detected by the at least one microphone and (b)generate a command-keyword event when the command-keyword enginedetects, in the input sound data, at least one of a plurality ofkeywords supported by the command-keyword engine; in response todetecting the first command keyword, making a first determination, via afirst local natural language unit (NLU), whether the input sound dataincludes at least one keyword within a first a first predeterminedlibrary of keywords from which the first NLU is configured to determinean intent of a given voice input; receiving an indication of a seconddetermination, made by a second NLU, whether the input sound dataincludes at least one keyword from a second predetermined library ofkeywords; comparing the results of the first determination with thesecond determination; and based on the comparison, foregoing furtherprocessing of the input sound data.

Example 9: The method of any one of the preceding Examples, furthercomprising: detecting, via the command-keyword engine, a second commandkeyword in a second voice input represented in second input sound data;in response to detecting the second command keyword, making a thirddetermination, via the first local NLU, that the second input sound dataincludes one or more keywords from the first predetermined library ofkeywords; receiving an indication of a fourth determination made by thesecond NLU that the second input sound data includes one or morekeywords from the second predetermined library of keywords; comparingthe results of the third determination with the fourth determination;and based on the comparison, performing a command according to one ormore parameters corresponding to the at least one keyword in the secondinput sound data.

Example 10: The method of any one of the preceding Examples, whereincomparing the results of the third determination with the fourthdetermination comprises confirming one or more keywords of the thirddetermination are identical to the one or more keywords of the fourthdetermination.

Example 11: The method of any one of the preceding Examples, whereinreceiving an indication of the second determination made by the secondNLU comprises receiving, over a local area network via the networkinterface, the indication from a second playback device having thesecond NLU.

Example 12: The method of any one of the preceding Examples, wherein:the playback device comprises a plurality of microphones; the first NLUdetects, in input sound data detected by a first subset of themicrophones, keywords from the first predetermined library of keywords;and the second NLU detects, in input sound data detected by a secondsubset of the microphones, keywords from the second predeterminedlibrary of keywords.

Example 13: The method of any one of the preceding Examples, wherein thefirst predetermined library of keywords includes one or more keywordsthat are not included in the second predetermined library of keywords.

Example 14: The method of any one of the preceding Examples, wherein theplayback device further comprises a voice assistant service (VAS)wake-word engine configured to receive input sound data representing thesound detected by the at least one microphone and generate a VASwake-word event when the VAS wake-word engine detects a VAS wake word inthe input sound data, wherein the functions further comprise streamingsound data representing the sound detected by the at least onemicrophone to one or more servers of the VAS when the VAS wake-wordevent is generated.

Example 15: A tangible, non-transitory computer-readable medium storinginstructions that, when executed by one or more processors, cause theprocessors to perform functions comprising: the method of any one of thepreceding Examples.

Example 16: A playback device of a media playback system, the playbackdevice comprising: at least one speaker; one or more microphonesconfigured to detect sound; a network interface; one or more processors;and data storage having instructions stored thereon that are executableby the one or more processors to cause the playback device to performfunctions comprising: receiving input sound data representing the sounddetected by the one or more microphones; detecting, via acommand-keyword engine, a first command keyword in a first voice inputrepresented in the input sound data, wherein the command-keyword engineis configured to (a) process input sound data representing the sounddetected by the at least one microphone and (b) generate acommand-keyword event when the command-keyword engine detects, in theinput sound data, one of a plurality of keywords supported by thecommand-keyword engine; in response to detecting the first commandkeyword, determining, via a first local natural language unit (NLU),whether the input sound data includes at least one keyword within afirst predetermined library of keywords from which the first NLU isconfigured to determine an intent of a given voice input; transmitting,via the network interface over a local area network, the input sounddata to a second playback device of the media playback system, thesecond playback device employing a second local NLU with a secondpredetermined library of keywords from which the second NLU isconfigured to determine an intent of a given voice input; receiving, viathe network interface, a response from the second playback device; andafter receiving the response from the second playback device, performingan action based on an intent determined by at least one of the first NLUor the second NLU according to the one or more particular keywords inthe voice input.

Example 17: The playback device of any one of the preceding Examples,wherein the first predetermined library of keywords includes keywordsthat are not included within the second predetermined library ofkeywords.

Example 18: The playback device of any one of the preceding Examples,wherein: the first predetermined library of keywords comprises a firstpartition having a first subset of keywords and a second partitionhaving a second subset of keywords different from the first subset ofkeywords; the second predetermined library of keywords comprises a thirdpartition having a third subset of keywords and a fourth partitionhaving a fourth subset of keywords; wherein the first subset of keywordsand the third subset of keywords include some or all of the samekeywords; wherein the third subset of keywords differs from the first,second, and fourth subsets of keywords, and wherein the fourth subset ofkeywords differs from the first, second, and third subsets of keywords.

Example 19: The playback device of any one of the preceding Examples,wherein the first subset of keywords and the third subset of keywordsare identical, and include a plurality of keywords associated withplayback transport commands.

Example 20: The playback device of any one of the preceding Examples,wherein the transmitting the input sound data via the network interfaceto a second playback device of the media playback system comprisesselecting the second playback device from among a plurality ofadditional playback devices of the media playback system, wherein eachof the additional playback devices comprises a respective NLU configuredto detect, in input sound data, keywords from a respective predeterminedlibrary of keywords different from the other respective predeterminedlibraries of keywords from which each respective NLU is configured todetermine an intent of a given voice input, wherein the selection isbased at least in part on the input sound data.

Example 21: The playback device of any one of the preceding Examples,wherein the keywords of the first predetermined library of keywordsassociated with the first NLU comprises keywords corresponding to afirst intent category, and wherein the second predetermined library ofkeywords associated with the second NLU comprises keywords correspondingto a second intent category.

Example 22: The playback device of any one of the preceding Examples,further comprising a voice assistant service (VAS) wake-word engineconfigured to receive input sound data representing the sound detectedby the at least one microphone and generate a VAS wake-word event whenthe first wake-word engine detects a VAS wake word in the input sounddata, wherein the playback device streams sound data representing thesound detected by the at least one microphone to one or more servers ofthe voice assistant service when the VAS wake-word event is generated.

Example 23: A method comprising: receiving input sound data representingthe sound detected by one or more microphones of a playback device;detecting, via a command-keyword engine, a first command keyword in afirst voice input represented in the input sound data, wherein thecommand-keyword engine is configured to (a) process input sound datarepresenting the sound detected by the at least one microphone and (b)generate a command-keyword event when the command-keyword enginedetects, in the input sound data, one of a plurality of keywordssupported by the command-keyword engine; in response to detecting thefirst command keyword, determining, via a first local natural languageunit (NLU), whether the input sound data includes at least one keywordwithin a first predetermined library of keywords from which the firstNLU is configured to determine an intent of a given voice input;transmitting, via the network interface over a local area network, theinput sound data to a second playback device of the media playbacksystem, the second playback device employing a second local NLU with asecond predetermined library of keywords from which the second NLU isconfigured to determine an intent of a given voice input; receiving, viathe network interface, a response from the second playback device; andafter receiving the response from the second playback device, performingan action based on an intent determined by at least one of the first NLUor the second NLU according to the one or more particular keywords inthe voice input.

Example 24: The method of any one of the preceding Examples, wherein thefirst predetermined library of keywords includes keywords that are notincluded within the second predetermined library of keywords.

Example 25: The method of any one of the preceding Examples, wherein:the first predetermined library of keywords comprises a first partitionhaving a first subset of keywords and a second partition having a secondsubset of keywords different from the first subset of keywords; thesecond predetermined library of keywords comprises a third partitionhaving a third subset of keywords and a fourth partition having a fourthsubset of keywords; wherein the first subset of keywords and the thirdsubset of keywords include some or all of the same keywords; wherein thethird subset of keywords differs from the first, second, and fourthsubsets of keywords, and wherein the fourth subset of keywords differsfrom the first, second, and third subsets of keywords.

Example 26: The method of any one of the preceding Examples, wherein thefirst subset of keywords and the third subset of keywords are identical,and include a plurality of keywords associated with playback transportcommands.

Example 27: The method of any one of the preceding Examples, wherein thetransmitting the input sound data via the network interface to a secondplayback device of the media playback system comprises selecting thesecond playback device from among a plurality of additional playbackdevices of the media playback system, wherein each of the additionalplayback devices comprises a respective NLU configured to detect, ininput sound data, keywords from a respective predetermined library ofkeywords different from the other respective predetermined libraries ofkeywords from which each respective NLU is configured to determine anintent of a given voice input, wherein the selection is based at leastin part on the input sound data.

Example 28: The method of any one of the preceding Examples, wherein thekeywords of the first predetermined library of keywords associated withthe first NLU comprises keywords corresponding to a first intentcategory, and wherein the second predetermined library of keywordsassociated with the second NLU comprises keywords corresponding to asecond intent category.

Example 29: The method of any one of the preceding Examples, wherein theplayback device further comprises a voice assistant service (VAS)wake-word engine configured to receive input sound data representing thesound detected by the at least one microphone and generate a VASwake-word event when the first wake-word engine detects a VAS wake wordin the input sound data, wherein the functions further comprisestreaming sound data representing the sound detected by the at least onemicrophone to one or more servers of the voice assistant service whenthe VAS wake-word event is generated.

Example 30: A tangible, non-transitory computer-readable medium storinginstructions that, when executed by one or more processors, cause theprocessors to perform functions comprising: the method of any one of thepreceding Examples.

1. (canceled)
 2. A system comprising: a first playback device and asecond playback device, the first playback device comprising: one ormore first microphones; a first network interface; one or more firstprocessors; and first data storage having instructions stored thereonthat are executable by the one or more first processors to cause thefirst playback device to perform first functions comprising: receiving,based on a user voice utterance, first input sound data representing thesound detected by the one or more first microphones; making a firstdetermination, via a first local natural language unit (NLU), whetherthe first input sound data includes at least one keyword within a firstpredetermined library of keywords from which the first NLU is configuredto determine an intent of a given voice input; receiving, over a localarea network and via the first network interface, an indication of asecond determination made by a second NLU of the second playback device;and based on the indication of the determination made by the second NLU,forgoing further processing of the first input sound data; the secondplayback device comprising: one or more second microphones; a secondnetwork interface; one or more second processors; and second datastorage having instructions stored thereon that are executable by theone or more second processors to cause the second playback device toperform second functions comprising: receiving, in response to the uservoice utterance, second input sound data representing the sound detectedby the one or more second microphones; receiving, based on the uservoice utterance, second input sound data representing the sound detectedby the one or more second microphones; making the second determination,via the second local natural language unit (NLU), that the second inputsound data includes at least one keyword within a second predeterminedlibrary of keywords from which the second NLU is configured to determinean intent of a given voice input; transmitting, over a local areanetwork via the second network interface, an indication of the seconddetermination, to the first playback device.
 3. The system of claim 2,wherein: the first determination comprises determining that the firstinput sound data includes at first keyword with a first associatedconfidence score; the second determination comprises determining thatthe second input sound data includes the first keyword with a secondassociated confidence score higher than the first; and transmitting theindication of the second determination comprises transmitting the secondassociated confidence score.
 4. The system of claim 2, wherein thesecond functions further comprise performing a command according thedetermined at least one keyword.
 5. The system of claim 2, wherein thefirst functions further comprise transmitting, over the local areanetwork via the first network interface, an indication of the firstdetermination to the second playback device.
 6. The system of claim 5,wherein transmitting the indication of the first determination to thesecond playback device comprises transmitting an associated confidencescore.
 7. The system of claim 2, wherein the first predetermined libraryof keywords and the second predetermined library of keywords share atleast some keywords in common.
 8. The system of claim 2, wherein thefirst predetermined library of keywords includes one or more keywordsthat are not included in the second predetermined library of keywords.9. A method comprising receiving, based on a user voice utterance, firstinput sound data representing the sound detected by one or more firstmicrophones of a first playback device; receiving, based on the uservoice utterance, second input sound data representing the sound detectedby one or more second microphones of a second playback device; making afirst determination, via a first local natural language unit (NLU) ofthe first playback device, whether the first input sound data includesat least one keyword within a first predetermined library of keywordsfrom which the first NLU is configured to determine an intent of a givenvoice input; making a second determination, via a second local naturallanguage unit (NLU) of the second playback device, that the second inputsound data includes at least one keyword within a second predeterminedlibrary of keywords from which the second NLU is configured to determinean intent of a given voice input; transmitting, over a local areanetwork from the second playback device to the first playback device, anindication of the second determination; receiving, over a local areanetwork and at the first playback device, the indication of the seconddetermination made by the second NLU of the second playback device; andbased on the indication of the determination made by the second NLU,forgoing further processing of the first input sound data by the firstplayback device.
 10. The method of claim 9, wherein: the firstdetermination comprises determining that the first input sound dataincludes at first keyword with a first associated confidence score; thesecond determination comprises determining that the second input sounddata includes the first keyword with a second associated confidencescore higher than the first; and transmitting the indication of thesecond determination comprises transmitting the second associatedconfidence score.
 11. The method of claim 9, wherein the secondfunctions further comprise performing a command according the determinedat least one keyword.
 12. The method of claim 9, wherein the firstfunctions further comprise transmitting, over the local area network viathe first network interface, an indication of the first determination tothe second playback device.
 13. The method of claim 9, whereintransmitting the indication of the first determination to the secondplayback device comprises transmitting an associated confidence score.14. The method of claim 9, wherein the first predetermined library ofkeywords and the second predetermined library of keywords share at leastsome keywords in common.
 15. The method of claim 9, wherein the firstpredetermined library of keywords includes one or more keywords that arenot included in the second predetermined library of keywords.
 16. One ormore non-transitory computer-readable media storing instructions that,when executed by one or more processors of a system comprising first andsecond playback devices, cause the system to perform operationscomprising: receiving, based on a user voice utterance, first inputsound data representing the sound detected by one or more firstmicrophones of a first playback device; receiving, based on the uservoice utterance, second input sound data representing the sound detectedby one or more second microphones of a second playback device; making afirst determination, via a first local natural language unit (NLU) ofthe first playback device, whether the first input sound data includesat least one keyword within a first predetermined library of keywordsfrom which the first NLU is configured to determine an intent of a givenvoice input; making a second determination, via a second local naturallanguage unit (NLU) of the second playback device, that the second inputsound data includes at least one keyword within a second predeterminedlibrary of keywords from which the second NLU is configured to determinean intent of a given voice input; transmitting, over a local areanetwork from the second playback device to the first playback device, anindication of the second determination; receiving, over a local areanetwork and at the first playback device, the indication of the seconddetermination made by the second NLU of the second playback device; andbased on the indication of the determination made by the second NLU,forgoing further processing of the first input sound data by the firstplayback device.
 17. The one or more computer-readable media of claim16, wherein: the first determination comprises determining that thefirst input sound data includes at first keyword with a first associatedconfidence score; the second determination comprises determining thatthe second input sound data includes the first keyword with a secondassociated confidence score higher than the first; and transmitting theindication of the second determination comprises transmitting the secondassociated confidence score.
 18. The one or more computer-readable mediaof claim 16, wherein the second functions further comprise performing acommand according the determined at least one keyword.
 19. The one ormore computer-readable media of claim 16, wherein the first functionsfurther comprise transmitting, over the local area network via the firstnetwork interface, an indication of the first determination to thesecond playback device.
 20. The one or more computer-readable media ofclaim 16, wherein transmitting the indication of the first determinationto the second playback device comprises transmitting an associatedconfidence score.
 21. The one or more computer-readable media of claim16, wherein the first predetermined library of keywords and the secondpredetermined library of keywords share at least some keywords incommon.